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INTRODUCTION — Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited disorder caused by a genetic defect in the red blood cell (RBC) enzyme G6PD, which generates NADPH and protects RBCs from oxidative injury. G6PD deficiency is the most common enzymatic disorder of RBCs.
The severity of hemolytic anemia varies among individuals with G6PD deficiency, making diagnosis more challenging in some cases. Identification of G6PD deficiency and patient education regarding safe and unsafe medications and foods is critical to preventing future episodes of hemolysis.
This topic review discusses the clinical manifestations, diagnosis, and management of G6PD deficiency. Separate topic reviews discuss the pathogenesis of G6PD deficiency and an overall approach to the patient with unexplained hemolytic anemia.
●Pathophysiology and genetics of G6PD deficiency – (See "Genetics and pathophysiology of glucose-6-phosphate dehydrogenase deficiency".)
●Diagnostic approach to the child with hemolytic anemia – (See "Overview of hemolytic anemias in children".)
●Diagnostic approach to the adult with hemolytic anemia – (See "Diagnosis of hemolytic anemia in the adult".)
EPIDEMIOLOGY — G6PD deficiency is the most common enzymatic disorder of red blood cells (RBCs), affecting 400 million people worldwide [1-3].
G6PD deficiency is global in its distribution (figure 1) . It occurs most often in the tropical and subtropical zones of the Eastern Hemisphere (eg, Africa, Europe, Asia) [5,6]. The following prevalences have been reported:
●Kurdish Jews – 60 to 70 percent 
●Sardinia – 4 to 35 percent, depending on the village 
●South African Blacks – 20 percent 
●Thailand – 17 percent 
●African Americans – 11 to 12 percent [11,12]
●Brazilian Blacks – 8 percent 
●Greeks – 6 percent 
●South China – approximately 6 percent 
●India – 3 percent 
●Japan and Korea – 0 to 1 percent [17,18]
This geographic distribution is highly correlated with regions in which malaria was once endemic, leading to the hypothesis that G6PD deficiency may have conferred a selective advantage against infection by Plasmodium falciparum, similar to observations with other RBC abnormalities. (See "Protection against malaria in the hemoglobinopathies" and "Protection against malaria by abnormalities in red cell surface antigens and cytoskeletal proteins".)
G6PD deficiency is an X-linked disorder. As a result, males who inherit a G6PD mutation are hemizygous for the defect; all of their RBCs are affected. (See "Overview of Mendelian inheritance", section on 'Sex-linked inheritance'.)
Females who inherit a heterozygous G6PD mutation usually do not have severe hemolytic anemia, since half of their RBCs express the normal G6PD allele and half express the abnormal allele. The majority of females who inherit an abnormality in G6PD are unaffected carriers. However, the cells that express the abnormal allele are as vulnerable to hemolysis as the enzyme-deficient RBCs in males. The presence of anemia will vary depending on the severity of deficiency in the affected cells and whether there is skewed X-inactivation (lyonization) that results in a greater expression from the abnormal allele in a large percentage of RBCs .
Homozygosity or compound heterozygosity for an abnormal G6PD gene has been reported in as many as 1 percent of American women [19-21]. These females are as severely affected as males.
CLASSIFICATION — Numerous G6PD variants have been described. These have been classified by the World Health Organization according to the magnitude of the enzyme deficiency and the severity of hemolysis [22,23]. This classification gives some approximation of the magnitude of hemolysis an individual might incur in the setting of an oxidative stress. Only class I, II, and III are of clinical significance.
●Class I – Class I variants have severe enzyme deficiency (eg, <10 percent of normal) associated with chronic hemolytic anemia.
●Class II – Class II variants also have severe enzyme deficiency (<10 percent of normal), but there is usually only intermittent hemolysis, typically on exposure to oxidant stress such as fava bean exposure or ingestion of certain drugs. G6PD Mediterranean is the classic example.
●Class III – Class III variants have moderate enzyme deficiency (10 to 60 percent of normal) with intermittent hemolysis, typically associated with significant oxidant stress. G6PD A- is the classic example.
●Class IV – Class IV variants have no enzyme deficiency or hemolysis. The wild-type (normal) enzyme is considered a class IV variant, as are numerous other genetic changes that do not alter levels of the enzyme. These variants are of no clinical significance.
●Class V – Class V variants have increased enzyme activity (more than twice normal). These are typically uncovered during testing for G6PD deficiency. They are of no clinical significance.
Certain variants are seen more commonly in certain populations:
●G6PD Mediterranean – The G6PD Mediterranean variant (563C>T) is the most common abnormal variant in Caucasians, particularly individuals from the Mediterranean region and the Middle East . It is a class II variant associated with severe hemolysis. The half-life of this variant is measured in hours. Thus, the majority of circulating RBCs have grossly deficient G6PD enzyme activity and will undergo hemolysis upon exposure to an oxidant injury. However, in the absence of oxidant stress, hemolysis typically does not occur and there is no anemia or reticulocytosis.
●G6PD A- – The G6PD A- variant (202G>A/376A>G) is the most common variant in individuals of African ancestry. It is a class III variant associated with mild to moderate hemolysis as well as sensitivity to the antimalarial drug primaquine. The enzymatic activity of this variant is normal in reticulocytes, but it declines more rapidly than the normal enzyme (half-life, 13 days, compared with 62 days for the normal enzyme) [24,25]. As a result, only the oldest RBCs undergo hemolysis upon exposure to oxidant stress.
●Variants in Asians – Several different G6PD variants occur in Asians .
•In China, three major variants are recognized. The most common is G6PD Canton (1376G>T), which is usually reported to be a class II variant, although sometimes it is considered to be in class III. Another common variant is G6PD Kaiping (1388G>A), which is usually classified as a class III variant although occasionally considered to be in class II. A third variant is G6PD Gaohe (95A>G), which is almost always considered to be a class II variant. These three variants account for over 70 percent of G6PD deficiency cases in China.
•The most common variant in Southeast Asia is G6PD Mahidol (487G>A), a class III variant.
•Of interest, although India borders China, none of the Chinese G6PD variants are found in India, where the most common type is G6PD Mediterranean (563C>T).
The genetics and pathophysiology of G6PD deficiency is discussed in more detail separately. (See "Genetics and pathophysiology of glucose-6-phosphate dehydrogenase deficiency", section on 'Classification of G6PD variants'.)
CLINICAL MANIFESTATIONS — The clinical expression of G6PD deficiency encompasses a spectrum of disease severity. The severity of disease and the likelihood of developing neonatal jaundice or chronic hemolysis, and the magnitude of hemolysis when hemolytic episodes occur, depends on the degree of the enzyme deficiency, which in turn is determined by the characteristics of the G6PD variant. (See 'Classification' above.)
●The majority of individuals are asymptomatic and do not have hemolysis in the steady state. They have neither anemia, evidence of increased red blood cell (RBC) destruction, nor an alteration in blood morphology, although a modest shortening of RBC survival can be demonstrated by isotopic techniques [27,28]. This includes almost all individuals with the most prevalent G6PD variants, G6PD A- and G6PD Mediterranean. However, episodes of acute hemolysis with hemolytic anemia may be triggered by medications, certain foods, and acute illnesses, especially infections. (See 'Acute hemolytic anemia' below.)
●Rarely, individuals with severe disease (class I variants) may have chronic hemolysis. (See 'Congenital nonspherocytic hemolytic anemia and chronic hemolysis' below.)
In most cases, women who have inherited one abnormal G6PD allele are unaffected carriers. However, as noted above, women who inherit a class I mutation, or those with skewed lyonization, may have clinical disease. Women who are homozygous or compound heterozygous for an abnormal G6PD gene will have a similar phenotype as men. (See 'Epidemiology' above.)
Acute hemolytic anemia — Some individuals with G6PD deficiency have episodes of acute hemolysis in the setting of oxidant injury from medications, acute illnesses, and certain foods. Once patients are diagnosed and are able to reduce oxidant stress exposures through medication avoidance, the frequency of hemolysis may decline dramatically. Episodes of acute hemolysis are more common in individuals with G6PD Mediterranean, which has a half-life measured in hours, than with G6PD A-, which has a half-life measured in days.
Typical presentation — The typical episode of hemolysis is illustrated by the course of an acute hemolytic episode following the administration of primaquine to an individual with G6PD A-, the variant most commonly seen in individuals of African ancestry . At two to four days after drug ingestion, there is the sudden onset of jaundice, pallor, and dark urine. There may be abdominal pain and/or back pain. Hemolysis may be mild and self-limiting in some individuals, and severe and life-threatening in others . This is associated with an abrupt fall in the hemoglobin concentration by 3 to 4 g/dL, during which time the peripheral blood smear reveals RBC fragments, microspherocytes, and eccentrocytes or "bite" cells (picture 1). Special stains can document the production of Heinz bodies, which are collections of denatured globin chains often attached to the RBC membrane. Hemolysis is both extravascular and intravascular. (See "Unstable hemoglobin variants", section on 'Hemoglobin precipitation and Heinz body formation'.)
The anemia induces an appropriate stimulation of erythropoiesis, with an increase in reticulocytes that is apparent within five days and is maximal at 7 to 10 days after the onset of hemolysis. These reticulocytes and younger RBCs have the highest levels of G6PD activity, often sufficient to withstand the oxidative stress of ongoing drug exposure. As a result, the acute hemolytic process ends after about one week, with ultimate reversal of the anemia, even with continued drug ingestion.
More severe hemolysis may be seen in individuals with G6PD Mediterranean, the variant most commonly seen in individuals from Mediterranean countries and the Middle East, as well as in other class II variants (see 'Classification' above). The anemia is more severe because a larger population of circulating RBCs is vulnerable to hemolysis, since the half-life of G6PD Mediterranean is shorter and fewer RBCs have sufficient G6PD activity to prevent oxidant injury. Hemolysis in these individuals may continue well after the drug is discontinued [31,32].
The clinical presentation of G6PD-deficient Asians is variable, depending whether the defect is a class II or III variant. (See 'Classification' above.)
Inciting drugs, foods, illnesses — Sources of oxidant injury that may elicit an episode of acute hemolysis in an individual with G6PD include a number of medications, as well as several foods and certain acute illnesses, especially infections. In a series of 102 patients with G6PD deficiency from 1966 that categorized 119 episodes of acute hemolysis, 46 (39 percent) were precipitated by a medication alone, and 73 (61 percent) appeared to be related solely to a concurrent illness .
●Medications and chemicals – Medications that can precipitate hemolysis in G6PD-deficient individuals are listed in the table (table 1) and on various websites (eg, www.g6pd.org, www.g6pddeficiency.org). Classic examples include the antibiotics primaquine and dapsone and the anti-uricemic drugs rasburicase and pegloticase. Additional chemicals such as henna compounds used in hair dyes and tattoos, aniline dyes, and naphthaline (found in moth balls and lavatory deodorants) may also cause hemolysis .
The common denominator of these drugs is their interaction with hemoglobin and oxygen, leading to the formation of H2O2 and other oxidizing radicals within RBCs [5,6,35,36]. As these oxidants accumulate within enzyme-deficient RBCs with low glutathione levels, hemoglobin and other proteins are oxidized, leading to cell lysis. (See "Genetics and pathophysiology of glucose-6-phosphate dehydrogenase deficiency", section on 'Pathophysiology of G6PD deficiency' and "Hemolytic anemia due to drugs and toxins".)
Conflicting information may be found regarding certain medications, such as those that modestly shorten the RBC lifespan. These may appear on some lists as "safe" and others as "unsafe" . One such example is sulfamethoxazole, a component of the commonly used trimethoprim-sulfamethoxazole [35,37,38]. Other drugs may have initially been labeled as "unsafe" when in fact hemolysis was caused by an infection that the drug was administered to treat (eg, aspirin).
●Foods – Certain foods can also trigger episodes of hemolysis in individuals with G6PD deficiency. Ingestion of fava beans is the classic example (picture 2). Acute intravascular hemolysis upon ingestion of fava beans, referred to as favism, occurs most commonly in male children between the ages of one and five years. Symptoms begin within 5 to 24 hours after ingestion and include headache, nausea, back pain, chills, and fever, and are followed by hemoglobinuria and jaundice . The fall in hemoglobin concentration is acute, often severe, and, in the absence of transfusion, can be fatal. Other foods such as bitter melon have also been implicated; these foods are listed below. (See 'Dietary restrictions' below.)
●Medical illnesses – Infection is the typical illness that causes hemolysis in G6PD-deficient individuals, and it is likely to be the most common inciting factor for hemolytic anemia once the individual is aware of the diagnosis and avoids oxidant medications. Hemolysis can occur with a variety of organisms (eg, viral, bacterial, rickettsial) and sites of infection (eg, pneumonia, hepatitis). Hemolytic anemia associated with infections can range from mild and self-limited to severe enough to cause acute renal failure [33,40-47]. In the series of patients from 1966, pneumonia was the most common inciting infection . In the setting of viral hepatitis, the combination of an increased bilirubin load from hemolysis and a damaged liver unable to process bilirubin as well as normal results in an exaggerated elevation in the serum bilirubin concentration.
The factors responsible for accelerated destruction of G6PD-deficient RBCs during infection are not known. One possible explanation is that the cells are damaged by oxidants generated by phagocytic macrophages .
Diabetic ketoacidosis has also been reported to precipitate hemolysis in individuals with G6PD deficiency, although one study of patients with the G6PD Mediterranean variant found no such correlation [33,49,50]. Both acidosis and hyperglycemia are potential precipitating factors, and correction of the abnormalities has been associated with reversal of the hemolytic process . In some diabetic patients, occult infection may be a common trigger for both acute hemolysis and ketoacidosis.
Neonatal jaundice — Anemia and jaundice are often first noted in the newborn period in individuals with severe G6PD deficiency. The degree of jaundice ranges from subclinical to severe; in severe cases, there is a risk of bilirubin-induced neurologic dysfunction and kernicterus (permanent neurologic damage) if the patient is not treated aggressively . (See "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Clinical manifestations'.)
Unlike neonatal jaundice seen in hemolytic disease of the fetus and newborn (HDFN), G6PD deficiency-related jaundice is rarely present at birth; the peak incidence of jaundice onset is two to three days after birth . Jaundice is more prominent than anemia, which is rarely severe.
The risk of neonatal hyperbilirubinemia associated with G6PD deficiency was illustrated in a 2015 meta-analysis of cohort studies that included 21,585 neonates, 877 of whom had hyperbilirubinemia . The relative risk of hyperbilirubinemia in neonates with G6PD deficiency was 3.92 (95% CI 2.13-7.20). Data from the USA Kernicterus Registry from 1992 to 2004, which were not included in the meta-analysis, indicate that over 30 percent of kernicterus cases are associated with G6PD deficiency . Thus, routine testing for G6PD deficiency is performed in many neonates with hyperbilirubinemia and/or those with less dramatic bilirubin elevations who are of Mediterranean, Nigerian, or East-Asian ancestry. (See 'Diagnostic evaluation' below and "Evaluation of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Additional evaluation'.)
Neonates with the rare class I variants are at greatest risk of neonatal jaundice; however, most infants with hyperbilirubinemia due to G6PD deficiency have more common variants and come from the Mediterranean region or Asia [55-58]. In one series of 43 cases from Italy, for example, 39 had G6PD Mediterranean, one had G6PD A-, and three had other variants . Among affected Chinese children, most cases are associated with G6PD Canton .
The risk of neonatal hyperbilirubinemia is less in African-Americans than that in Africans and Jamaicans, despite both groups generally having the same G6PD A- variant [59-61]. Untreated hyperbilirubinemia in African and Jamaican Black infants frequently leads to kernicterus with severe neurologic injury or death [60,62]. The difference in risk with the same G6PD variant is thought to be related to local customs and differences in oxidant exposure. In the United States, there is concern that changes in health care delivery with early discharge of newborn infants may increase the risk. One report described four newborn infants with G6PD deficiency (three African-American, and one mixed Peruvian/Chinese) who developed kernicterus following early hospital discharge, even though there was adherence to the early neonatal discharge guidelines of the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists . (See "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Kernicterus'.)
The cause of neonatal hyperbilirubinemia in G6PD-deficient infants is not clear [64,65]. It has been presumed that the combination of increased bilirubin production due to accelerated breakdown of RBCs and the immaturity of the liver is responsible [60,66,67]. Indirect evidence such as a lower incidence of neonatal hyperbilirubinemia in immigrants to the United States supports the importance of local environmental variables, although often there is no obvious oxidant exposure [68,69]. Possible exposures may include maternal ingestion of oxidant foods, herbs used in traditional Chinese medicine, and clothing impregnated with naphthalene [70,71]. Some neonates with G6PD Mediterranean have a partial defect in bilirubin glucuronide conjugation similar to that seen in Gilbert's disease . (See "Pathogenesis and etiology of unconjugated hyperbilirubinemia in the newborn".)
Congenital nonspherocytic hemolytic anemia and chronic hemolysis — Chronic hemolysis is not characteristic of most individuals with G6PD deficiency, but those with severe deficiency (eg, activity <10 percent at baseline) can have chronic hemolysis with or without chronic anemia. Variants that produce chronic hemolytic anemia are referred to as class I variants (see 'Classification' above). These individuals have such severe G6PD deficiency that they may have hemolysis even in the absence of oxidant injury from medications or illnesses [73-77].
These individuals may also be referred to as having congenital nonspherocytic hemolytic anemia. The term nonspherocytic is somewhat of a misnomer, since these individuals may have spherocytes on the peripheral blood smear. However, this term is useful in distinguishing individuals with G6PD deficiency, in whom spherocytes are relatively infrequent at baseline, from those with hereditary spherocytosis, in whom spherocytes are abundant. (See 'Differential diagnosis' below.)
Most individuals with chronic hemolysis have mild to moderate anemia (hemoglobin 8 to 10 g/dL) with a reticulocyte count of 10 to 15 percent. Pallor is uncommon, scleral icterus is intermittent, and splenomegaly is rare. Hemolysis can be exaggerated by exposure to drugs or chemicals with oxidant potential or exposure to fava beans . Some drugs with relatively mild oxidant potential that are safe in patients with class II or class III G6PD variants may increase hemolysis in patients with class I variants.
The typically mild degree of anemia reflects the ability of increased erythropoiesis to compensate for the hemolysis. Thus, as with other chronic hemolytic anemias, the anemia may be worsened by diminished erythropoietic capacity due to infection or to parvovirus-induced aplastic crises. Such a crisis may be the event that first leads to examination of the blood and establishment of diagnosis of G6PD deficiency. (See "Clinical manifestations and diagnosis of parvovirus B19 infection".)
Neutrophil dysfunction — G6PD is used by other cells besides RBCs to reduce oxidant injury. Rarely, individuals with severe G6PD deficiency (eg, <20 percent activity at baseline) may have neutrophil dysfunction due to an impaired respiratory burst, with impaired bactericidal activity and recurrent infections with catalase-positive organisms . Although this has been reported, in our clinical experience patients do not appear to be more susceptible to infections.
This subject is discussed in more detail separately. (See "Myeloperoxidase deficiency and other enzymatic WBC defects causing immunodeficiency", section on 'Glucose-6-phosphate dehydrogenase deficiency'.)
Indications for evaluation — Testing for G6PD deficiency may be appropriate in the following settings:
●Evaluation of neonatal jaundice or unexplained hemolytic anemia. (See 'Patients being evaluated for the cause of neonatal jaundice or hemolysis' below.)
●Asymptomatic individuals at high risk of G6PD deficiency prior to administration of certain medications. (See 'Patients at risk for G6PD deficiency who require treatment with an oxidant medication' below.)
●Certain other populations (eg, certain newborn screening settings or asymptomatic family members of affected individuals). (See 'Role of population screening' below and 'Genetic counseling and prenatal testing' below.)
Testing may be performed using an initial screening test followed by a confirmatory test, or using the confirmatory test initially, depending on available resources and institutional guidelines. (See 'Screening tests' below and 'Confirmatory tests' below.)
Patients being evaluated for the cause of neonatal jaundice or hemolysis — Testing for G6PD deficiency is appropriate in infants with unexplained neonatal jaundice and in an individual of any age with unexplained, direct antiglobulin (Coombs) test (DAT)-negative hemolytic anemia, especially those from families with a history of inherited anemia and those from populations most likely to be affected (eg, African, Southern European, Middle Eastern, or Southeast Asian heritage). (See 'Epidemiology' above.)
In those with a strong suspicion for G6PD deficiency, this testing may be done early in the evaluation. In others, it may be done following negative testing for more likely causes of unexplained anemia or hemolytic anemia. (See "Approach to the child with anemia" and "Approach to the adult patient with anemia" and "Diagnosis of hemolytic anemia in the adult".)
Patients at risk for G6PD deficiency who require treatment with an oxidant medication — Testing for G6PD deficiency is also appropriate for individuals who require treatment with oxidant drugs including dabrafenib, dapsone, chlorpropamide, glipizide, glyburide, methylene blue, pegloticase, primaquine, quinine, rasburicase, and others. A common example is a patient who requires presumptive anti-relapse therapy with primaquine to eradicate the liver stages of Plasmodium vivax or P. ovale. (See "Overview of non-falciparum malaria in nonpregnant adults and children", section on 'Preventing relapse' and "Prevention of malaria infection in travelers".)
In most cases, it is prudent to screen for G6PD deficiency if the clinician needs to use a drug that could potentially cause oxidant injury (eg, patients with HIV infection who require dapsone).
Testing for G6PD deficiency prior to administration of medicines that can produce oxidant injury is consistent with information provided in drug labeling by the US Food and Drug Administration, as summarized on an FDA website on pharmacogenetics . Specific drug label information should be consulted to determine whether patients with G6PD deficiency should consider the drug to be contraindicated or whether the drug can be administered with increased monitoring.
Timing of G6PD assay — An important aspect of G6PD diagnosis deficiency is that testing is based on direct measurements of G6PD activity in a population of RBCs. In the setting of an acute hemolytic episode, the RBCs with the most severely reduced G6PD activity will have hemolyzed, and thus their G6PD activity will not be measured in the assay. This situation can produce false-negative results in some patients who are tested in the midst of a severe hemolytic episode.
False-negative results are most likely to occur in individuals who have populations of RBCs that are severely G6PD-deficient and RBCs that are not severely deficient, such as individuals of African ancestry, in whom G6PD activity declines gradually as RBCs age, and women, most of whom are heterozygous and have a mixture of normal and G6PD-deficient RBCs. False-negative results are also most likely to be seen during the period of initial reticulocytosis, when there is the highest proportion of reticulocytes, which typically have normal G6PD activity.
Thus, if initial testing is negative and a suspicion for G6PD deficiency remains, testing should be repeated approximately three months after the hemolytic episode has resolved (ie, the typical time it takes for a new population of circulating RBCs to be produced). During this three-month period, it would be prudent to avoid potential sources of oxidant injury. (See 'Avoidance of unsafe drugs' below and 'Dietary restrictions' below.)
Screening tests — A number of screening tests are available for G6PD deficiency . These assays all work by assaying the normal function of the enzyme, reduction of NADP (nicotinamide adenine dinucleotide phosphate) to NADPH (figure 2), which is the initial step in the hexose monophosphate (HMP, also called pentose phosphate) shunt. For the most part these tests are semiquantitative. Thus, if positive they typically should be followed by a quantitative confirmatory test. (See 'Confirmatory tests' below.)
The following methodologies for measuring enzyme activity may be used:
●Fluorescent spot test – This is the simplest, most reliable, and most sensitive of the G6PD screening tests [81-83]. It is based upon the fluorescence of NADPH after glucose-6-phosphate and NADP are added to a hemolysate of the patient's RBCs.
●Methemoglobin reduction test – This test estimates NADPH generation indirectly by measuring the transfer of hydrogen ions from NADPH to an methemoglobin using methylene blue [80,84]. When combined with a technique for the elution of methemoglobin from intact cells, this test can detect relative G6PD sufficiency in individual RBCs, permitting detection of the carrier state with approximately 75 percent accuracy .
●Point-of-care tests – The need for point-of-care tests to be used on-site (eg, prior to administration of antimalarial drugs) has been emphasized by various groups. Available tests that can be performed on a fingerstick and scored visually (ie, that do not require additional equipment in order to get the result) have been reviewed .
Point-of-care enzyme testing in potentially affected infants is being assessed as a means of risk reduction for neonatal kernicterus . (See "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Kernicterus'.)
Additional testing that is consistent with G6PD deficiency includes a positive Heinz body prep or glutathione (GSH) stability test; however, these tests are not specific for G6PD deficiency and should not be used for diagnosis or screening unless more specific tests are unavailable.
Confirmatory tests — Confirmatory testing is performed for individuals with a positive screening test, and in some cases as the initial test, depending on available resources, cost, and institutional practices. These tests assay NADPH formation quantitatively.
The quantitative tests are performed by adding a measured amount of RBC hemolysate to an assay mixture that contains substrate (glucose-6-phosphate) and a cofactor (NADP); the rate of NADPH generation is measured spectrophotometrically (absorbance at a wavelength of 340 nanometers) [88,89].
Results are expressed as units of enzyme activity per gram of hemoglobin. Normal ranges may differ depending on the methodology used and the assay temperature.
●Typical normal range at 25°C – 5.5 to 8.8 units/gram of hemoglobin
●Typical normal range at 37°C – 8.0 to 13.46 units/gram of hemoglobin
Levels of G6PD are higher in the newborn than they are in the adult [21,90]. When higher-than-normal levels are seen in older patients, this almost invariably reflects the presence of a young RBC population with reticulocytosis. Rarely, high activity G6PD variants have been reported, but we do not evaluate for these unless there are extenuating circumstances and the possibility of reticulocytosis has been eliminated. (See 'Classification' above.)
Confirmatory testing using molecular/genetic/DNA methods is also available, although this approach is not used routinely. Testing for pathogenic G6PD variants is not particularly useful in the assessment of G6PD-deficient individuals of African or Mediterranean background. However, in Chinese patients where the severity of hemolysis can be variable, molecular studies may be helpful in predicting G6PD class, and thereby assessing potential hemolytic risk. Molecular testing may also be appropriate when it is necessary to identify a heterozygous female with borderline enzyme activity. There are several academic/commercial labs available for gene studies, which are listed on the GeneTests website.
Role of population screening — The question of whether testing for G6PD deficiency should be included in newborn screening programs worldwide has been raised . This screening has not been widely implemented; however, routine newborn screening is done in some populations with a high incidence of G6PD deficiency. (See "Newborn screening".)
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of G6PD deficiency includes other causes of hemolytic anemia and other causes of neonatal jaundice:
●Inherited hemolytic anemias – Other inherited hemolytic anemias include other enzyme deficiencies (eg, pyruvate kinase [PK]), hemoglobinopathies (eg, thalassemia, sickle cell disease), and membrane/cytoskeletal defects (eg, hereditary spherocytosis [HS]). Like G6PD deficiency, these can present with varying degrees of direct antiglobulin (Coombs)-negative hemolysis (with increased reticulocytes, decreased haptoglobin, increased lactate dehydrogenase [LDH], and anemia), and like G6PD deficiency, these may not be diagnosed until adulthood (or may be misclassified), especially if hemolysis is mild. Like many of these inherited disorders, G6PD deficiency is seen at greater frequency in populations from regions where malaria was once endemic, likely due to a protective effect. Unlike these other inherited hemolytic anemias, G6PD deficiency is characterized by low G6PD enzyme activity at baseline, and testing such as hemoglobin analysis, osmotic fragility, and band 3 flow cytometry will be normal in individuals with G6PD deficiency. (See "Overview of hemolytic anemias in children", section on 'Intrinsic hemolytic anemias' and "Diagnosis of hemolytic anemia in the adult".)
●Acquired hemolytic anemias – Acquired hemolytic anemias include a number of immune and non-immune causes of hemolysis. Like G6PD deficiency, in some cases an acute medical illness or exposure to a drug may precede hemolysis. Like G6PD deficiency, these can present with varying degrees of hemolysis (with increased reticulocytes, decreased haptoglobin, increased LDH, and anemia). Unlike these acquired conditions, G6PD deficiency is characterized by low G6PD enzyme activity at baseline, and testing such as hemoglobin analysis and osmotic fragility will be normal in individuals with G6PD deficiency. (See "Overview of hemolytic anemias in children", section on 'Extrinsic hemolytic anemias' and "Diagnosis of hemolytic anemia in the adult" and "Hemolytic anemia due to drugs and toxins".)
●Conditions causing neonatal hyperbilirubinemia – Neonatal hyperbilirubinemia can be caused by a number of conditions associated with increased bilirubin production (eg, hemolytic disease of the fetus and newborn [HDFN]) or decreased bilirubin clearance (eg, anatomic obstruction, metabolic disorders affecting bilirubin clearance). Like G6PD deficiency, these conditions may be associated with anemia and neonatal jaundice. Unlike G6PD deficiency, these conditions may be more likely to present with hyperbilirubinemia at birth (versus two to three days after birth for G6PD deficiency), and these other conditions are associated with normal G6PD enzyme activity. (See "Pathogenesis and etiology of unconjugated hyperbilirubinemia in the newborn".)
MANAGEMENT — The cornerstone of management of G6PD deficiency is the avoidance of oxidative stress to red blood cells (RBCs). This is usually straightforward once the diagnosis is known. However, there may be instances in which an oxidant drug is absolutely required, or cases in which oxidative stress comes from an infection or other acute medical condition that cannot be avoided. In these settings, management depends on the severity of hemolysis and anemia and the patient's age and comorbidities.
Treatment of neonatal jaundice and chronic hemolysis — The management of neonatal jaundice due to G6PD deficiency does not differ from that recommended for neonatal jaundice arising from other causes. Mild cases generally do not require treatment; intermediate cases require phototherapy; and severe cases may require exchange transfusion. (See "Treatment of unconjugated hyperbilirubinemia in term and late preterm infants".)
For those rare individuals with chronic hemolysis, routine supplementation with folic acid is reasonable. In such cases, a dose of 1 mg daily is adequate. For G6PD-deficient individuals who do not have chronic hemolysis, there is no need for supplemental folic acid.
Treatment of acute hemolytic episodes — Whenever hemolysis occurs in an individual with G6PD deficiency, any inciting agent(s) should be removed as soon as possible .
Other interventions may include aggressive hydration for acute intravascular hemolysis or transfusion for severe anemia. (See "Indications and hemoglobin thresholds for red blood cell transfusion in the adult".)
Various treatments directed at the source of oxidant injury or NADPH production have been evaluated and found to be ineffective (eg, xylitol, vitamin E) [5,28,92,93].
Avoidance of unsafe drugs — The principle intervention for reducing hemolysis in individuals with G6PD deficiency is avoiding exposure to drugs known to trigger hemolysis. Commonly implicated drugs are listed in the table (table 1) and updated on G6PD websites listed above. (See 'Inciting drugs, foods, illnesses' above.)
There may be certain settings in which it is especially important to give one of these drugs, and this may be possible in individuals with mild hemolysis (eg, class III variants) (see 'Classification' above). As an example, primaquine has been given to individuals with the G6PD A- variant as long as a low dose is used (15 mg/day or 45 mg once or twice weekly) and the complete blood count (CBC) is monitored closely . The mild anemia that may ensue is corrected by the compensatory increase in reticulocyte production and does not recur unless the dose of the drug is escalated.
Data regarding dietary supplements and herbs are challenging to evaluate. In a 2016 systematic review of published reports, no evidence of harms were observed for vitamin C, vitamin E, vitamin K, ginkgo biloba, or alpha-lipoic acid . We neither prescribe nor proscribe any of these supplements for our G6PD-deficient patients. Just as for any questionable food, we ask our patients and their families to be observant of any changes suggestive of increased hemolysis (change in stamina, scleral icterus, dark [cola-colored] urine) associated with the use of supplements.
Dietary restrictions — It has also been suggested that affected individuals should avoid ingestion of fava beans, also referred to as "broad beans," which can cause hemolysis in some but not all affected individuals . However, unlike certain medications that induce hemolysis in all individuals with G6PD deficiency, sensitivity to the fava bean is more variable.
The G6PD variant most commonly implicated in favism is G6PD Mediterranean and G6PD Canton. Thus, favism occurs most often in people from Italy, Greece, North Africa, the Middle East, and Asia . Africans and African-Americans with G6PD deficiency are much less susceptible, although there are very rare cases of favism associated with the African variant, G6PD A- . In addition, the response to the bean by the same individual at different times may not be consistent . Other genetic factors, perhaps related to the hepatic metabolism of potentially oxidant compounds within the fava bean, may play a role in determining the severity of the reaction [98-100]. For reasons that are unknown, favism occurs mostly in children .
Favism most often results from the ingestion of fresh (rather than preserved) fava beans (picture 2). Consequently, the peak seasonal incidence of favism in Mediterranean regions coincides with harvesting of the bean during April and May . However, equally severe hemolysis can occur after consuming fried fava beans, a popular Chinese snack (picture 2). Favism also has been reported in nursing infants whose mothers have eaten fava beans.
A question that often comes up relates to the safety of falafel, a common Middle Eastern food. The answer depends on the ingredients. Egyptian falafel is made from fava beans, whereas falafel made elsewhere in the world is usually made from chick peas, which are considered safe for people with G6PD deficiency. However, in some areas, falafel is made from a mixture of fava beans and chick peas. The easiest response to the question is that G6PD-deficient individuals should not consume anything with fava beans. However, since not everyone with G6PD deficiency, particularly adults, is sensitive to fava beans, we advise patients to use cautious observation.
Favism can also occur following ingestion of bitter melon. Also, several other foods such as blueberries are listed on the internet as potentially associated with hemolysis, although the direct relationship is not clear. In our practice we do not advise dietary restrictions; however, for any questionable food we emphasize to our patients and their families to be observant of any changes suggestive of increased hemolysis. Patients are encouraged to call their physician if any changes are noted.
The mechanism by which fava beans induce hemolysis may involve the pyrimidine metabolites divicine and isouramil (aglycones of the glucosides) [102-104]. These compounds act as strong reducing agents. Both rapidly overwhelm the already diminished GSH-generating capacity of G6PD-deficient cells and may also have direct effects on RBC function. In vitro studies have shown that divicine reduces the activity of catalase which, like the glutathione pathway, contributes to hydrogen peroxide removal, and requires NADPH for maintenance of normal activity .
Pregnancy — Pregnant and nursing women who are heterozygous for G6PD deficiency should avoid drugs with oxidant potential, because some of these drugs gain access to the fetal circulation and to breast milk.
Blood donation — As a general rule, donated blood is not screened for G6PD deficiency, and individuals with G6PD deficiency can donate blood, as long as they are otherwise able to donate and do not have anemia. This is because the typical lifespan of transfused G6PD-deficient RBCs is thought to be relatively normal, and it is unlikely for a patient to be transfused with multiple units of G6PD-deficient blood and have clinically significant hemolysis, even in areas of high prevalence . (See "Blood donor screening: Procedures and processes to enhance safety for the blood recipient and the blood donor".)
One exception may be blood used for exchange transfusion of newborn infants, which poses a theoretical risk if a large enough volume of G6PD-negative cells is transfused. (See "Red blood cell transfusions in the newborn" and "Red blood cell transfusion in infants and children: Administration and complications".)
Genetic counseling and prenatal testing — G6PD deficiency is an X-linked disorder. Affected males have a 100 percent chance of transmitting the abnormal gene to their daughters, who will be heterozygous. Affected females have a 50 percent chance of transmitting the defect to their sons and daughters (figure 3). In general, males who inherit an abnormal G6PD gene are more likely to have clinically significant disease, and heterozygous females are likely to be unaffected carriers. However, females can have hemolysis if they have skewed lyonization or if they are homozygous or compound heterozygous for an abnormal G6PD gene, which can happen in populations with a high prevalence of G6PD deficiency. (See 'Epidemiology' above.)
Prenatal testing for G6PD deficiency is not routinely performed. (See "Initial prenatal assessment and first-trimester prenatal care".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Basics topic (see "Patient education: Glucose-6-phosphate dehydrogenase deficiency (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common inherited red blood cell (RBC) enzymatic defect, affecting 4 million people worldwide (figure 1). Individuals of certain groups are at higher risk, including Kurdish Jews; South African, Brazilian, and African-American Blacks; and people from Thailand, Sardinia, Greece, South China, and India (eg, those in areas where malaria was once endemic). G6PD deficiency is an X-linked disorder. Males are more likely to be affected, and heterozygous females are typically unaffected carriers, but females who are homozygous, compound heterozygous, or heterozygous with skewed lyonization can have clinically significant hemolysis. (See 'Epidemiology' above.)
●Clinically significant G6PD variants are classified as class I, II, or III by presence (class I) or absence of chronic hemolysis and the severity of reduction in enzyme activity (<10 percent for class II; 10 to 60 percent for class III). (See 'Classification' above.)
●Clinical manifestations of G6PD deficiency include acute hemolytic anemia, typically induced by medications (table 1), chemicals (eg, henna, naphthaline), foods (eg, fava beans (picture 2)), or illnesses (typically, infections) that cause oxidant injury. Most individuals have only intermittent episodes of hemolysis, but more severely affected individuals can have severe and even life-threatening neonatal jaundice and/or chronic hemolytic anemia. (See 'Clinical manifestations' above.)
●Evaluation for G6PD deficiency is appropriate in individuals with unexplained neonatal jaundice or direct antiglobulin (Coombs)-negative hemolytic anemia, and in high-risk individuals prior to treatment with known oxidant medications (table 1). First degree relatives of affected individuals and certain other populations may also benefit from testing. (See 'Indications for evaluation' above.)
●Available testing includes semi-quantitative screening tests, some of which can be read at the point-of-care, and quantitative tests that report units of G6PD enzyme activity per gram of hemoglobin. The principle of these assays is generation of NADPH by RBCs (figure 2). False-negative results may occur in some individuals in the setting of acute hemolysis because the most severely G6PD-deficient cells have been destroyed; in such cases testing should be repeated three months after the hemolytic episode has resolved. DNA testing is available but not used routinely. (See 'Timing of G6PD assay' above and 'Screening tests' above and 'Confirmatory tests' above.)
●The differential diagnosis of G6PD deficiency includes a number of other inherited and acquired hemolytic anemias and causes of neonatal jaundice. (See 'Differential diagnosis' above.)
●Management of patients with G6PD deficiency depends on the severity of the deficiency and the clinical setting. Specific recommendations for neonatal jaundice, acute hemolytic episodes, chronic hemolysis, and avoidance of unsafe medications and foods are presented above. Pregnancy is generally well-tolerated, and individuals with G6PD deficiency can donate blood as long as they are not anemic. (See 'Management' above.)
●The genetic changes and pathophysiology of G6PD deficiency are presented in detail separately. (See "Genetics and pathophysiology of glucose-6-phosphate dehydrogenase deficiency".)
●A general approach to the evaluation of patients with hemolytic anemia is also presented separately. (See "Overview of hemolytic anemias in children" and "Diagnosis of hemolytic anemia in the adult".)
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