Patient information: Diabetes mellitus type 1: Overview

TYPE 1 DIABETES OVERVIEW

Type 1 diabetes mellitus is a chronic medical condition that occurs when the pancreas, an organ in the abdomen, produces very little or no insulin (figure 1). Insulin is a hormone that helps the body to absorb and use glucose and other nutrients from food, store fat, and build up protein. Without insulin, blood glucose (sugar) levels become elevated.

Elevated blood sugar levels (called hyperglycemia) cause a person to urinate more frequently, causing loss of body water and dehydration. You may also feel tired and lose weight. In addition, a serious and potentially life-threatening complication known as diabetic ketoacidosis can develop (see 'Symptoms' below. Long term complications associated with hyperglycemia can affect the eyes, nerves, kidneys, and cardiovascular system, leading to blindness, loss of sensation in the feet, the need for amputation of toes or a foot, kidney failure, and an increased risk of heart attack and stroke.

Type 1 diabetes requires regular blood sugar monitoring and treatment with insulin. Treatment, lifestyle adjustments, and self-care can effectively control blood sugar levels and minimize your risk of ketoacidosis and other disease-related complications.

Type 1 diabetes usually begins in childhood or young adulthood, but can develop at any age. In the United States, Canada, and Europe, type 1 diabetes accounts for 5 to 10 percent of all cases of diabetes. It is relatively more common in people who are white compared to people of African or Asian descent.

Other topics that discuss type 1 diabetes are also available. (See "Patient information: Diabetes mellitus type 1: Insulin treatment" and "Patient information: Self-blood glucose monitoring in diabetes mellitus" and "Patient information: Type 1 diabetes mellitus and diet" and "Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus".) and (see "Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus".

THE IMPACT OF TYPE 1 DIABETES

Being diagnosed with type 1 diabetes can be a frightening and overwhelming experience for some patients, and it is common to have questions about why it developed, what it means for long-term health, and how it will affect everyday life. For most patients, the first few months after being diagnosed are filled with emotional highs and lows. People with newly-diagnosed diabetes, as well as their families, can use this time to learn as much as possible so that diabetes-related care (eg, self-blood sugar testing, medical appointments, daily insulin) becomes a "normal" part of the daily routine. (See "Patient information: Self-blood glucose monitoring in diabetes mellitus".)

In addition, people who are newly diagnosed should talk to their healthcare provider about resources that are available for medical as well as psychological support. This may include group classes, meetings with a nutritionist, social worker, or nurse educator, and other educational resources such as books, web sites, or magazines. Several of these resources are listed in this topic review (see 'Where to get more information' below.

Despite the risks associated with type 1 diabetes, most people can lead active lives and continue to enjoy the foods and activities that they previously enjoyed. Diabetes does not mean an end to special occasion foods like birthday cake, and with a little advanced planning, most people with diabetes can enjoy exercise in almost any form.

TYPE 1 DIABETES CAUSES

Type 1 diabetes usually develops when a person's immune system destroys the insulin-producing cells (called the beta cells) in the pancreas. This is called an autoimmune response. The cause of the abnormal immune response that destroys the beta cells is being actively studied.

This process occurs over many months or years, during which there may be no signs or symptoms of diabetes. High blood sugar and its associated symptoms (frequent urination, thirst) do not usually occur until more than 90 percent of the beta cells have been destroyed, which greatly reduces the amount of insulin in the body.

Type 1 diabetes may develop in people with a family history of type 1 diabetes, but may also develop in people with no family history of diabetes. In either case, the person has one or more genes that make them susceptible to the disease. Environmental factors, such as exposure to certain viruses and foods early in life, may trigger the autoimmune response.

TYPE 1 DIABETES RISK FACTORS

A person whose parent or sibling has type 1 diabetes is at increased risk of developing the disease, compared to a person with no family history (5 to 6 percent versus 0.4 percent, respectively).

To determine if a person with a family history of type 1 diabetes is at increased risk, genetic testing can be performed. However, these tests are currently only available to people who participate in a clinical research trial. Anyone who is found to be at risk for developing type 1 diabetes may be enrolled in further clinical trials aimed at preventing or delaying the disease from developing.

TYPE 1 DIABETES DIAGNOSIS

The diagnosis of diabetes is based upon a person's symptoms and the results of laboratory tests.

Symptoms — Most people have symptoms of high blood sugar levels (hyperglycemia) before being diagnosed with type 1 diabetes. These symptoms may include excessive thirst, fatigue, frequent urination, weight loss, or blurred vision.

Less commonly, a person will develop signs and symptoms of diabetic ketoacidosis (DKA) at the time of diagnosis. DKA causes symptoms of high blood sugar levels (see above), as well as nausea and vomiting, abdominal pain, rapid breathing, lethargy, decreased alertness, and sometimes coma. DKA is a medical emergency and must be treated promptly.

Rarely, type 1 diabetes is diagnosed before symptoms develop.

Laboratory tests — Several blood tests are used to measure blood sugar levels; this is the primary test for diagnosing diabetes. Additional tests can determine the type of diabetes and its severity.

• Random blood sugar test — For a random blood sugar test, blood can be drawn at any time throughout the day, regardless of when you last ate. A random blood sugar level of 200 mg/dL (11.1 mmol/L) or higher in a person who has the typical symptoms of hyperglycemia (see 'Symptoms' above) suggests a diagnosis of diabetes.
• Fasting blood sugar test — Fasting blood sugar testing involves measuring the blood sugar level after not eating or drinking for 8 to 12 hours (usually overnight). Fasting blood sugar is normally less than 100 mg/dL (5.6 mmol/L); values of 126 mg/dL (7.0 mmol/L) or higher suggests diabetes. However, the test must be repeated on another day to confirm the diagnosis of diabetes.
• Hemoglobin A1C test (A1C) — The A1C blood test measures the average blood sugar level during the past two to three months. It is used to monitor blood sugar control in people with known diabetes, but is not usually used to diagnose the disease.

Normal values for A1C are usually 6.1 percent or lower (indicating an average blood sugar of 120 mg/dL [6.6 mmol/L]) (table 1). Most healthcare providers recommend measuring A1C three to four times per year in people with type 1 diabetes.

Criteria for diagnosis — The following criteria are used to define blood sugar levels as normal or indicative of diabetes.

• Normal — Fasting plasma glucose (FPG) <100 mg/dL (5.6 mmol/L).
• Diabetes mellitus — A person is diagnosed with diabetes if he or she has one or more of the following criteria:

• - Symptoms of diabetes (see 'Symptoms' above) and a fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher
• - Symptoms and a random blood sugar of 200 mg/dL (11.1 mmol/L) or higher

The blood tests must be repeated on another day to confirm that they remain abnormally high.

Type 1 versus type 2 diabetes — A healthcare provider is usually able to determine whether a patient has type 1 or type 2 diabetes based upon the need for insulin (which is needed from the beginning in type 1, and less commonly early in type 2), and the presence of ketones in the urine when blood sugar levels are elevated (common in type 1, uncommon in type 2).

Other factors, such as age at diagnosis (generally younger for type 1), obesity (more common in type 2), and the presence of antibodies in the blood (present in type 1) can be used to distinguish between the two types. (See "Patient information: Diabetes mellitus type 2: Overview".)

However, there are situations where it is not clear if a person has type 1 or 2 diabetes. In this situation, a healthcare provider usually treats the patient as if they have type 1, since missing this diagnosis can result in DKA.

TYPE 1 DIABETES PREVENTION

Methods to prevent type 1 diabetes are still in the investigational stage. Currently, no treatment has been found to be effective in preventing type 1 diabetes for more than a brief period of time.

TYPE 1 DIABETES TREATMENT

Treatment of diabetes requires a team approach, including the patient and their family and healthcare providers (physician, nurse, diabetes educator, dietitian), and sometimes other clinicians (exercise physiologist, podiatrist, etc). The treatment of type 1 diabetes is discussed on a separate topic review. (See "Patient information: Diabetes mellitus type 1: Insulin treatment".)

LONG-TERM OUTCOMES WITH TYPE 1 DIABETES

Several studies have proven that persons with diabetes whose blood sugar levels are kept at near-normal levels can reduce their risk of long-term complications. In the Diabetes Control and Complications Trial, patients were followed for more than 6 years. Half the group used intensive insulin therapy (either with an insulin pump or three or more insulin injections daily) with the goal of maintaining sugar levels as close to the non-diabetic range as possible. The other half used conventional therapy (one to two insulin injections per day).

Intensive therapy reduced the risk of retinopathy by more than 75 percent, nephropathy by more than 50 percent, and neuropathy by 60 percent [1]. Longer-term study of the DCCT population has shown that heart disease and strokes are also reduced with intensive diabetes therapy.

Thus, people with diabetes can greatly reduce their risk of long-term complications by monitoring blood sugar levels frequently and using intensive insulin therapy. The goal A1C is as close to the non-diabetic range as possible and, at a minimum, should be less than 7 percent.

TYPE 1 DIABETES COMPLICATIONS

Complications of type 1 diabetes are related to the disease itself as well as to the treatments that are necessary to manage diabetes. (See "Patient information: Preventing complications in diabetes mellitus".)

Disease-related complications — People with type 1 diabetes are at increased risk of cardiovascular disease, which can cause myocardial infarction (heart attack), angina (chest pain), stroke, and death. The risk is estimated to be at least twice that of nondiabetics.

However, you can substantially lower your risk of cardiovascular disease by not smoking, taking a low-dose aspirin every day (for adults only), and by managing high blood pressure and hyperlipidemia with diet, exercise, and medications, and by achieving an A1C level of 7 percent or lower. (See "Patient information: High cholesterol and lipids (hyperlipidemia)" and "Patient information: High blood pressure treatment in adults" and "Patient information: Smoking cessation" and "Patient information: Aspirin and cardiovascular disease".)

The more specific complications of type 1 diabetes include damage to small blood vessels (called microvascular damage) and nerves. This damage is the result of elevated blood sugar levels over a period of many years; improving blood sugar control can prevent or reduce the risk of these complications.

Microvascular damage affects the retina in the eyes (the light-sensitive film in the back of the eyes). This is called retinopathy, which can lead to decreased vision or blindness. Microvascular damage also affects the kidneys (called nephropathy, which can lead to kidney failure), and nerves (called neuropathy, which can cause pain and increases the risk of foot injury and infection).

The risk of nephropathy, neuropathy, and retinopathy is related to the level of the A1C; the higher the A1C value, the greater your risk (graph 1 and graph 2). Other factors, especially high blood pressure, increase the risk of diabetic complications. (See "Patient information: Foot care in diabetes mellitus".)

Treatment-related complications — Treatment-related complications of type 1 diabetes are more common in people who use intensive insulin therapy. Intensive insulin therapy involves giving three or more insulin injections daily, or use of an insulin pump. Complications of this type of treatment can include hypoglycemia (low blood sugar) and weight gain. However, intensive insulin therapy has significant benefits despite these treatment-related risks. (See "Patient information: Diabetes mellitus type 1: Insulin treatment".)

Results from a large trial demonstrated that the risk of low blood sugar increased as the A1C was lowered (graph 1). Each patient must find his or her own level of tolerance for episodes of low blood sugar. (See "Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus".)

Weight gain is also a common problem with intensive insulin regimens. Weight gain can be prevented or managed with regular exercise and careful attention to diet.

PREGNANCY AND TYPE 1 DIABETES

Women with type 1 diabetes are usually able to become pregnant and have a healthy baby. However, it is important to tightly control blood sugar levels before and during pregnancy to minimize the risk of complications. A full discussion of this topic is available separately. (See "Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus".)

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Diabetes mellitus type 1: Insulin treatment
Patient information: Self-blood glucose monitoring in diabetes mellitus
Patient information: Type 1 diabetes mellitus and diet
Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus
Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus
Patient information: Diabetes mellitus type 2: Overview
Patient information: Preventing complications in diabetes mellitus
Patient information: High cholesterol and lipids (hyperlipidemia)
Patient information: High blood pressure treatment in adults
Patient information: Smoking cessation
Patient information: Aspirin and cardiovascular disease
Patient information: Foot care in diabetes mellitus

Professional Level Information:
Amylin analogs for the treatment of diabetes mellitus
Blood glucose self-monitoring in management of diabetes mellitus
Classification of diabetes mellitus and genetic diabetic syndromes
Diagnosis of diabetes mellitus
Effects of exercise in diabetes mellitus in adults
Estimation of blood glucose control in diabetes mellitus
General principles of insulin therapy in diabetes mellitus
Glycemic control and vascular complications in type 1 diabetes mellitus
Glycemic control in women with type 1 and type 2 diabetes mellitus during pregnancy
Insulin secretion and pancreatic beta-cell function
Insulin therapy in type 1 diabetes mellitus
Management of hypoglycemia during treatment of diabetes mellitus
Microalbuminuria in type 1 diabetes mellitus
Nutritional considerations in type 1 diabetes mellitus
Overview of diabetic nephropathy
Overview of medical care in adults with diabetes mellitus
Pancreas and islet transplantation in diabetes mellitus

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/healthtopics.html)

• National Institute of Diabetes and Digestive and Kidney Diseases

      (www.niddk.nih.gov)

• American Diabetes Association (ADA)

      (800)-DIABETES (800-342-2383)
      (www.diabetes.org)

• The Endocrine Society

      (www.endo-society.org)

• The Hormone Foundation

       (www.hormone.org/public/diabetes.cfm, available in English and Spanish)

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