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Chronic urticaria: Diagnosis, theories of pathogenesis, and natural history
All topics are updated as new evidence becomes available and our peer review process is complete.
Literature review current through: Mar 2012. | This topic last updated: Dec 22, 2011.

INTRODUCTION — Chronic urticaria (CU) is defined by the presence of urticaria (hives), on most days of the week, for a period of six weeks or longer. No external cause can be identified in 80 to 90 percent of adults and children with CU [1-3]. There are several theories regarding the pathogenesis of idiopathic CU, none of which have been conclusively established.

Terminology — In this review, the terms chronic urticaria and chronic idiopathic urticaria are used synonymously. About 40 percent of patients with CU have accompanying angioedema, which typically affects the lips, cheeks, periorbital areas of the face, extremities, and genitals [4]. Here, the term CU includes patients with isolated urticaria, as well as those with accompanying angioedema.

The epidemiology, diagnosis, and theories of pathogenesis of chronic urticaria will be reviewed here. The management of chronic urticaria and the various syndromes of physical urticaria are discussed separately. (See "Chronic urticaria: Standard management and patient education" and "Physical urticarias".)

EPIDEMIOLOGY — At any given time, CU affects up to 1 percent of the general population in the United States, and the prevalence is believed to be similar in other countries [5,6]. Both children and adults can develop CU, although it is more common in adults. Women are affected twice as often as men [6-12], and the condition typically begins in the third to fifth decades of life [6,8,11].

EVALUATION AND DIAGNOSIS — CU is diagnosed clinically, by the recurrence of characteristic lesions for six weeks or longer. A detailed history and physical examination are essential in patients with persistent urticaria [13-16].

History — The history should include the characteristics of the lesions (eg, pruritic, burning, appearance), duration of individual lesions, and accompanying angioedema. The duration of the lesions is often difficult for patients to assess, and we sometimes suggest that patients trace a circle in pen around a newly developed lesion and time the period of resolution. Patients should also be asked about whether the lesions resolve without any residual “bruise” or pigmentation (aside from bruising caused by scratching). Lesions lasting longer than 24 hours and those that are painful or leave residual bruising are suggestive of a vasculitic process (See 'Biopsy' below.)

Appearance of lesions — Patients whose symptoms have resolved sometimes have difficulty describing urticarial lesions in a sufficiently detailed manner to assist in diagnosis. In this setting, showing patients photographs of urticaria and asking if their lesions looked similar can be helpful (picture 1 and picture 2 and picture 3).

No external cause can be identified in 80 to 90 percent of adults and children with CU, as mentioned previously [1-3,17]. Despite this, patients should be questioned about any newly administered drugs, including antibiotics, NSAIDS, and hormones [18,19]. Inquiries should be made about recent travel, infections, changes in health status, other atopic conditions, sexual history, and complete review of systems. The various identifiable causes of urticaria are discussed in more detail elsewhere. (See "New onset urticaria: Epidemiology, clinical manifestations, and etiologies".)

Patients should be thoroughly questioned about signs and symptoms of systemic disease, such as fever, weight loss, arthralgias, arthritis, cold or heat sensitivity, abdominal pain, and bone pain [20,21]. Occasionally, urticaria or urticarial vasculitis will be a presenting feature of an underlying systemic disorder. (See "New onset urticaria: Epidemiology, clinical manifestations, and etiologies", section on 'Systemic disorders that may include urticaria'.)

Laboratory evaluation — When the clinical history does not suggest an underlying etiology, routine laboratory tests are unlikely to be helpful [22-25]. Investigational tests are discussed separately. (See 'Theories of pathogenesis' below.)

  • In a systematic review of studies in which patients with CU were evaluated for underlying medical disorders, 29 studies including 6462 patients were examined [25]. Potentially causative internal diseases were identified in 1.6 percent, and there was no association between the number of tests ordered and the identification of an underlying disorder.
  • In one study of 125 patients with CU, abnormal routine laboratory or radiographic studies were found in 21 percent of subjects [26]. The majority of these abnormalities were evident from the initial history and physical examination, although it was concluded that a CBC with differential and erythrocyte sedimentation rate (ESR) (or other measures of acute phase reactants) were cost-effective screening tests for systemic diseases. Both tests are normal in the majority of cases of chronic urticaria, although an elevation of ESR of a few points is also common in uncomplicated CU.

    Significant elevations in ESR or C reactive protein (CRP) should prompt further investigation for systemic diseases, such as autoimmune, rheumatologic, infectious, or neoplastic diseases. Such an evaluation may include measurement of antinuclear antibodies (ANA), thyroid peroxidase antibody, cryoglobulins, hepatitis B and C serologies, and a serum protein electrophoresis. (See "Acute phase reactants".)
  • Another authority in the field has suggested that a thyroid stimulating hormone (TSH) level and a test of anti-thyroid antibodies (either antithyroglobulin or antimicrosomal) may be helpful to detect adult patients with associated thyroid autoimmunity [27]. Autoimmune thyroid disease is uncommon in children with CU [28]. (See "Pathogenesis of Hashimoto's thyroiditis (chronic autoimmune thyroiditis)".)
  • Eosinophilia should prompt evaluation for an atopic disorder or parasitic infection. (See "Approach to the patient with eosinophilia".)

Suggested tests — Based upon the above studies and observations, we suggest initially obtaining a complete blood count with differential, a CRP or ESR, and a TSH level, as general screening tests for the disorders that are most commonly associated with urticaria. Some clinicians also obtain thyroid autoantibodies (antithyroglobulin, antimicrosomal antibodies, or both), while others do so only if the TSH level is abnormal. Further testing should be based upon the results of these tests [22,23].

Biopsy — A three mm punch biopsy of an early lesion should be performed to rule out urticarial vasculitis in patients with one or more of the following features:

  • Individual lesions that persist beyond 24 hours, are painful rather than pruritic, have accompanying petechial or purpuric characteristics, or leave residual pigmentation upon resolution [16,29]
  • An elevated CRP/ESR and/or systemic symptoms
  • Symptoms that are unresponsive to antihistamines

Biopsy should also be obtained in patients with any features suggestive of cutaneous mastocytosis (see "Clinical manifestations, pathogenesis, and classification of mastocytosis (cutaneous and systemic)").

The biopsy sample should be obtained from a fresh lesion. Patients receiving glucocorticoids may need to discontinue these medications for several days in order to allow new lesions to form. Biopsy specimens should be submitted in formalin for routine hematoxylin and eosin (H&E) staining and in those patients in whom urticarial vasculitis is a strong consideration, in Michel’s media or freshly snap frozen for direct immunofluorescence microscopy. Consider testing for immunoglobulins in lesional skin when vasculitis is a strong consideration and in perilesional, non-involved skin when considering autoimmune blistering disease.

Biopsy findings — The pathology of chronic urticaria is somewhat heterogeneous among patients. However, biopsies consistently show interstitial edema with a perivascular mixed infiltrate, consisting of lymphocytes, eosinophils, and in some areas, a few neutrophils or basophils. Lymphocytes are generally CD4+ T lymphocytes. B lymphocytes are not usually seen [4]. Neutrophil-predominant urticaria is a variant of chronic urticaria that is often refractory to standard pharmacologic treatments, but biopsy should not show vasculitis. The significance of neutrophil-predominant urticaria, in terms of treatment or prognosis, is not known. Angioedema, if present, often shows a similar infiltrate and is characterized by more prominent edema of the interstitial tissues.

Leukocytoclasis should not be present in chronic urticaria. Leukocytoclasis is the fragmentation of neutrophils resulting in scattered nuclear fragments (nuclear dust) in the infiltrate, red blood cell extravasation within the lumen of affected vessels or in the interstitium, and fibrinoid degeneration of the endothelial cells resulting in a blunted vascular outline with fibrin deposits. If leukocytoclasis is seen, then the diagnosis of leukocytoclastic vasculitis and associated conditions must be considered. (See "Urticarial vasculitis", section on 'Histology' and 'Differential diagnosis' below.)

A dense cellular infiltrate consisting almost entirely of neutrophils, combined with the finding of true leukocytoclasis, but not vasculitis, should prompt evaluation for the rare disorder neutrophilic urticarial dermatosis. (See "Neutrophilic dermatoses".)

Several other disorders in the differential diagnosis for CU may also show a predominance of neutrophils, such as Schnitzler's syndrome, delayed pressure urticaria, and the Cryopyrin-Associated Periodic Syndromes (CAPS). Biopsies in these disorders may also mistakenly be interpreted as leukocytoclastic vasculitis. (see 'Differential diagnosis' below).

DIFFERENTIAL DIAGNOSIS — Several systemic disorders can present with urticaria-like lesions in the context of other signs and symptoms.

  • Systemic lupus erythematosus — Urticaria and urticarial vasculitis are among the many reported cutaneous manifestations of systemic lupus erythematosus. This disorder is reviewed in detail elsewhere. (See "Mucocutaneous manifestations of systemic lupus erythematosus".)
  • Cryoglobulinemia — Cryoglobulinemia causing cold-induced urticarial or vasculitic lesions can be seen in hepatitis C infection. Lesions are more prominent on the buttocks and lower extremities. (See "Overview of cryoglobulins and cryoglobulinemia" and "Cryopyrin-associated periodic syndromes and related disorders".)
  • Urticarial vasculitis — Urticarial vasculitis should be considered when the hives are painful rather than pruritic, last longer than 48 hours, leave residual pigmentation changes, or recur whenever glucocorticoids are tapered (picture 4 and picture 5). This disorder may occur in patients previously diagnosed with other systemic inflammatory diseases, such as Sjögren's syndrome or systemic lupus erythematosus (SLE). (See "Urticarial vasculitis".)
  • Mastocytosis — Mastocytosis includes a variety of disorders that are characterized by the overproliferation and accumulation of tissue mast cells. The cutaneous form of this disorder may present with lesions of urticaria pigmentosa (picture 6). These are pigmented papules that demonstrate the distinctive Darier's sign, wheals that appear with mild trauma, such as gentle stroking. Biopsy of these lesions reveals a focal collection of mast cells and requires a thorough evaluation for systemic mastocytosis. (See "Clinical manifestations, pathogenesis, and classification of mastocytosis (cutaneous and systemic)".)
  • Polymorphic eruption of pregnancy — Polymorphic eruption of pregnancy (PEP, also called pruritic urticarial papules and plaques and papules of pregnancy or PUPPP) is a pruritic dermatitis affecting pregnant women, which typically presents as erythematous papules within abdominal striae with periumbilical sparing. The lesions then spread to the extremities and coalesce to form urticarial plaques. The face, palms, and soles are usually spared. Lesions may also be target-like. PEP is reviewed elsewhere. (See "Dermatoses of pregnancy".)
  • Schnitzler's syndrome — Schnitzler's syndrome has been described in patients with a monoclonal IgM or IgG component (monoclonal gammopathy) who have associated fever, weight loss, bone pain, adenopathy, and urticaria, presumably due to circulating immune complexes and complement activation [30,31]. (See "Cutaneous manifestations of internal malignancy".)
  • Hypereosinophilic syndrome — Hypereosinophilic syndrome refers to a group of disorders characterized by persistent overproduction of eosinophils that infiltrate and damage tissues. Cutaneous symptoms include recurrent urticaria and angioedema. The diagnosis requires blood eosinophilia of ≥1500/microliter, present for more than six months, signs and/or symptoms of eosinophil-mediated end-organ dysfunction, and no other apparent etiologies for eosinophilia, such as parasitic infection or allergic disease. (See "Clinical manifestations, pathophysiology, and diagnosis of the hypereosinophilic syndromes".)
  • Cryopyrin-associated periodic syndromes — The cryopyrin-associated periodic syndromes (CAPS) include two syndromes that involve urticarial eruption: Familial cold autoinflammatory syndrome and the Muckle-Wells syndrome. These are rare genetic disorders. Familial cold autoinflammatory syndrome presents with periodic fever, urticaria, leukocytosis, conjunctivitis, and muscle and skin tenderness after exposure to cold. The onset of symptoms occurs during infancy in most cases. This disorder is discussed elsewhere.

    The Muckle-Wells syndrome involves periodic urticarial eruptions and is associated with mutations in cryopyrin. It has a similar phenotype to familial cold autoinflammatory syndrome except that patients are not cold sensitive and experience frequent sensorineural hearing loss. These disorders are reviewed in more detail elsewhere. (See "Cryopyrin-associated periodic syndromes and related disorders".)
  • Malignancy — There are intermittent case reports of malignancies presenting with urticarial-like lesions [32-34]. However, these patients rarely have simple urticaria and typically have urticarial lesions with prominent vasculitic properties, or they present with a variety of accompanying systemic symptoms. Diffuse and refractory pruritus or angioedema, without urticaria, represent other cutaneous manifestations of malignancy. (See "Cutaneous manifestations of internal malignancy".)

THEORIES OF PATHOGENESIS — None of the theories of pathogenesis of CU have been fully established [35]. The best-developed hypotheses include the autoimmune theory, theories involving histamine releasing factors, and the cellular defects theory. Hypotheses for which there is less evidence include abnormalities in the coagulation system and chronic infections.

Autoimmune theory — The concept that CU could represent an autoimmune disorder arose from the recognition that thyroid dysfunction and thyroid autoantibodies are more prevalent in patients with CU [21,36,37]. This led to a search for autoantibodies and other serum factors that could be responsible for increased release of histamine from cutaneous mast cells and basophils.

Association with autoimmune disorders — Thyroid autoantibodies, specifically thyroid peroxidase antibodies or antimicrosomal antibodies, are more commonly recognized among patients with CU (12 to 30 percent), compared to members of the general population (5 to 10 percent) [7,36-38]. Other autoimmune conditions, such as connective tissue diseases, vitiligo, and pernicious anemia, have also been recognized in patients with CU [21,25,39]. (See "Pathogenesis of Hashimoto's thyroiditis (chronic autoimmune thyroiditis)" and "Pathogenesis of Graves' disease".)

The presence of urticaria does not necessarily correlate with thyroid function; patients who are euthyroid, hypothyroid, or hyperthyroid may have urticaria or angioedema [21,40]. The majority of patients with chronic urticaria who have circulating thyroid autoantibodies have normal thyroid function [37]. These patients are often poorly responsive to standard therapies for urticaria and may have more persistent disease [39]. The role of these autoantibodies in patients with normal thyroid function is not clear. Their presence may simply reflect an underlying tendency to develop autoantibodies [39].

Based upon the association between chronic urticaria and thyroid autoimmunity, several studies have examined the use of thyroid supplementation therapy in the treatment of CU, with mixed results. These studies are reviewed separately. (See "Chronic urticaria: Standard management and patient education".)

Autologous serum skin test — Another line of investigation suggesting that CU is an autoimmune disorder was introduced in the 1980s with the description of the "autologous serum skin test" (ASST) [41]. The ASST involves intradermal injection of patients' own serum [41,42]. In preparation for this test, patients must refrain from taking antihistamines for three to seven days (depending upon the half-life of the specific drug), which can cause an exacerbation in symptoms.

In up to one-half of patients with CU, the intradermal injection of serum produces a wheal and flare reaction (ie, area of cutaneous edema and erythema) at the site of injection within 30 minutes (note that the time to maximal reaction is longer than 15 minutes seen in allergen skin testing) [43]. The ASST is proposed to provide an in vivo assay of serum factor-induced mast cell activation, since mast cells are difficult to collect and culture. (See "Mast cells: Development, identification, and physiologic roles".)

Problems with the ASST — The leading evidence against the clinical significance of the ASST is the fact that it is not unique to this CU [44-46]. In one study, positive ASSTs were found in 53 percent of patients with CU, 20 percent of patients with nonallergic asthma/rhinitis, and 56 percent of healthy controls [46].

In addition, the positivity of the ASST persists in patients with CU, even when the disorder is in clinical remission [47,48]. Finally, the ASST has not demonstrated clinical utility in identifying patients whose disease responds differently to treatment or carries a different prognosis [28,49,50].

Histamine releasing factors in the serum — The sera of patients with CU and positive ASSTs are capable of causing in vitro histamine release from basophils collected from control subjects [41]. It was therefore proposed that an autoantibody or other histamine releasing factor was present in the serum of these patients. However, it is important to note that the in vitro manipulation of basophils poses several technical challenges. (See 'Problems in studying basophils' below.)

Subsequent efforts to determine which component of the serum was responsible for the positive ASST revealed several possible candidate molecules [42,47,51,52]:

  • Human IgG molecules directed against the IgE receptor alpha subunit (anti-FcεR1alpha)
  • Human IgG molecules directed against the Fc region of IgE (anti-IgE)
  • Other low molecular weight molecules (10 to 15 kilodaltons)

The presence of autoantibodies to the IgE receptor or the Fc region of IgE can be demonstrated in as many as 30 to 50 percent of children and adults with CU [4,53-57]. These IgG molecules can trigger histamine release when incubated with normal basophils [51], and can activate mast cells, possibly through a mechanism involving complement [4,17,58-62]. However, the in vivo relevance of these autoantibodies has not been established [63], as IgG depleted serum can also induce a positive ASST [47]. In addition, autoantibodies to the IgE receptor or the Fc region of IgE have been identified in people without hives. (See 'Problems with the ASST' above.)

In summary, several histamine releasing factors have been identified in the serum, both immunoglobulins and low molecular weight molecules, but no one factor has been shown to be essential for a positive ASST result.

Histamine releasing factors in the plasma — Histamine releasing factors in the plasma have also been proposed. Some patients with chronic idiopathic urticaria demonstrate excessive or abnormal production of platelet-derived clotting factors, such as thrombin, possibly resulting from activation of the extrinsic pathway of the clotting cascade [64-66]. In one study, the plasma of 28 patients with CU contained higher levels of the polypeptide F1+2, which is produced upon activation of prothrombin to thrombin, compared to control plasma [64]. The levels of this peptide correlated with the severity of the patients' urticaria. Thrombin, in turn, is capable of activating mast cells and basophils, and also increasing the permeability of blood vessels [67-69]. In addition, thrombin can stimulate the generation of C5a, which has been shown to enhance IgG-dependent mast cell histamine release in patients with CU [62]. Other groups have also found abnormalities in the coagulation system that correlate with CU severity [70].

The identification of abnormalities in clotting factors lead to the autologous plasma skin test (APST), a variant of the ASST in which sodium citrate-anticoagulated plasma is injected intradermally [64]. The APST has reported to be positive in 40 to 86 percent of patients with CU, and it is not clear if this test provides information that is different from that of the ASST [64,71]. The APST has not yet been studied in patients with other conditions or in normal controls.

The finding that the extrinsic pathway of the clotting cascade activated in CU is consistent with reports of successful treatment of CU with the anticoagulant warfarin, in a small double-blind, placebo-controlled, crossover study of patients refractory to antihistamines [72]. Subcutaneous heparin was also reported to be effective in one patient [73]. (See "Chronic urticaria: Standard management and patient education", section on 'Other therapies for specific clinical situations'.)

Evidence against histamine-releasing factors — Similar to the ASST, anti-Fcε RI-alpha antibodies have been identified in other autoimmune diseases, even in the absence of urticaria, including pemphigus vulgaris, systemic lupus erythematosus, dermatomyositis, and pemphigoid, suggesting that they may represent an epiphenomenon [58,74,75]. In addition, the levels of autoantibodies in chronic urticaria do not appear to change with the clinical activity of the disease [76].

Assays are commercially available for detecting anti-FcεRI-alpha antibodies (eg, the Chronic Urticaria Index test; IBT labs), although these are based on poorly standardized basophil-activation tests and may be positive in healthy subjects [77]. (See 'Problems in studying basophils' below.)

In addition from issues with testing for, and specificity of autoimmune factors in CU, it remains unclear why such serologic factors would activate only skin mast cells, rather than more generalized mast cell and basophil activation leading to anaphylaxis, yet patients with CU are not at increased risk for anaphylaxis.

Cellular defects theory — The cellular defects theory generally proposes that patients with CU have defects in mast cell and/or basophil trafficking, signaling, and/or function.

  • Mast cell numbers are normal in the skin of patients with CU, although the cells release histamine more readily than cells from healthy controls in response to compounds that trigger nonimmunologic mast cell degranulation, such as 48/80 and codeine sulfate [78,79].
  • Peripheral blood basophil counts are low in patients with CU and lower with more severe disease, a finding attributed to increased migration of basophils to the skin [80-83].
  • Several groups identified functional differences in basophils from patients with CU. Although the cells contained normal amounts of histamine [84,85], histamine release was reduced following in vitro activation through the IgE receptor, although not with activation through other receptors [79,86,87]. Subsequently, two basophil phenotypes were identified in patients with CU: one type with an apparently normal response to IgE receptor activation ("responders"), and another type of basophil that does not respond to IgE-mediated activation ("nonresponders") [84]. These phenotypes are present in approximately equal numbers in patients with CU, unlike in normals, where "nonresponders" comprise only about 10 to 15 percent of the whole. The nonresponder phenotype demonstrates elevated intracellular levels of regulatory proteins that normally inhibit signaling through the IgE receptor. Finally, normalization in basophil responsiveness has been demonstrated in patients with CU as their symptoms improve, unlike levels of autoantibodies or ASST status [76,87].

Problems in studying basophils — Several issues arise in studying the basophils of subjects with CU:

  • Patients' basophils are typically obtained for study from peripheral blood, although it has not been established that circulating basophils are fully representative of cutaneous basophils, and the two populations may have different characteristics in this disorder.
  • Alternatively, basophils from normal donors may be used to test serum from chronic urticaria subjects, although this approach is also problematic due to the challenges in studying basophils:

  • Different labs using different basophil donors will yield different results with the same tested serum.
  • Basophils from individual donors can show variability in response to the same serum over time.
  • There are no standardized procedures for handling basophils for use in serum testing, including uniform approaches to cell isolation, dilution of serum, or addition of a basophil priming cytokine (ie, IL-3) to the assay mix.
  • Histamine release from normal donor basophils in response to CU serum may be due to several factors, such as activated complement, chemokines, or even IL-3 in the tested sample. Thus, the readout of the assay itself represents a complex cellular response that can be elicited through a variety of mechanisms.

Infectious agents — Attempts have been made to associate some common chronic infections with CU, including Helicobacter pylori [88-91], hepatitis A [92], and hepatitis C [93]. However, the evidence is largely anecdotal [94].

Foods and food additives — Up to 50 percent of adult patients with CU initially perceive food-associated reactions; however, in one study, only 10 percent of these individuals demonstrated signs or symptoms with placebo-controlled challenges [95]. IgE-mediated food allergy is far more likely to present with acute urticaria as part of generalized allergic reactions. In contrast, patients with CU will often report that rich meals, fermented foods, alcohol, and dramatic changes in diet will worsen the condition temporarily. This may be related to the histamine content or innate histamine-releasing properties of these foods, as well as the vasodilatory effects of alcohol and certain spices.

Food additives are rarely, if ever, confirmed to cause or contribute to flares of CU in carefully performed studies. Studies of food additives as an etiology of acute and chronic urticaria are reviewed elsewhere. (See "Allergic and asthmatic reactions to food additives".)

NATURAL HISTORY AND PROGNOSIS — CU is an episodic and self-limited disorder in most patients. The average duration of disease is two to five years [5,96]. In patients in whom no trigger or underlying disorder is identified, there is a rate of spontaneous remission at one year of approximately 30 to 50 percent [3,97]. However, symptoms persist beyond five years in nearly one-fifth of patients [9,98].

Duration of disease appears to correlate with symptom severity [96,98]. Symptoms persisted for longer in a prospective study of 228 patients with moderate to severe disease [96]. This study also found that in this subgroup, the presence of systemic hypertension was associated with longer disease duration. Among hypertensive patients, symptoms persisted for up to two and five years in 81 and 74 percent, respectively compared to 63 and 54 percent in normotensive patients. The type of antihypertensive medication administered did not appear to impact duration of urticaria. This finding warrants further study.

Another prospective study followed 139 patients with CU of all severities for five years and assessed disease duration, the presence of angioedema, and various laboratory parameters [98]. CU persisted beyond one and five years in 70 and 14 percent of patients, respectively. A longer duration of symptoms was associated with increased severity, the presence of angioedema, thyroid autoimmunity, and a positive ASST [39,98]. However, other studies have not found an association between positive ASST and persistent disease [3]. Thus, symptom severity appears to correlate with duration of CU, but the predictive value of other clinical and laboratory features requires further study.

SUMMARY AND RECOMMENDATIONS

  • Chronic urticaria (CU) is defined by the presence of urticaria (hives), on most days of the week, for a period of six weeks or longer. CU prevalence is up to 1 percent of the general population. Adults are affected more often than children, and women, more often than men. (See 'Epidemiology' above.)
  • The diagnosis is made clinically, based on the history and physical examination. No external cause can be identified in 80 to 90 percent of adults and children with CU. Laboratory studies are normal in most patients, although a complete blood count with differential, a CRP or ESR, and a TSH level are suggested. Biopsy of a fresh lesion is indicated in some circumstances. (See 'Evaluation and diagnosis' above.)
  • Several theories regarding the pathogenesis of chronic idiopathic urticaria have been proposed, although the data for each are incomplete and none appears to be helpful for determining treatment or prognosis. The best developed hypotheses involve histamine releasing factors and defects in basophil signaling and/or function. (See 'Theories of pathogenesis' above.)
  • Tests used in investigations of pathogenesis include the autologous serum and plasma skin tests, assays for autoantibodies directed against IgE or the FcepsilonRI receptor, and in vitro assessments of basophil function. However, these tests lack specificity and prognostic value for CU, are not standardized, and cannot be recommended for routine clinical use. (See 'Theories of pathogenesis' above.)
  • CU is a self-limited disease. Spontaneous remission occurs in 30 to 50 percent of patients by one year, although nearly one-fifth of patients still have symptoms after five years. Those with more severe symptoms may have longer lasting disease. (See 'Natural history and prognosis' above.)

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