Patient information: Diabetes mellitus type 2: Overview

INTRODUCTION

Type 2 diabetes mellitus occurs when the pancreas (an organ in the abdomen) produces insufficient amounts of the hormone insulin and/or the body's tissues become resistant to normal or even high levels of insulin (figure 1). This causes high blood glucose (sugar) levels, which can lead to a number of complications if untreated.

Type 2 diabetes is a chronic medical condition that requires regular monitoring and treatment. Treatment, which includes lifestyle adjustments, self-care measures, and sometimes medications, can control blood sugar levels in the near-normal range and minimize the risk of diabetes-related complications.

In the United States, Canada, and Europe, type 2 diabetes accounts for about 90 percent of all cases of diabetes. More than 6 percent of all people between the ages of 20 and 74 years and more than 12 percent of people over age 40 have type 2 diabetes; these numbers continue to increase.

Topics that discuss other aspects of type 2 diabetes are also available. (See "Patient information: Diabetes mellitus type 2: Treatment" and "Patient information: Diabetes mellitus type 2: Insulin treatment" and "Patient information: Type 2 diabetes mellitus and diet" and "Patient information: Self-blood glucose monitoring in diabetes mellitus" and "Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus" and "Patient information: Diabetes mellitus type 2: Alcohol, exercise, and medical care" and "Patient information: Preventing complications in diabetes mellitus".)

THE IMPACT OF DIABETES

Being diagnosed with type 2 diabetes can be a frightening and overwhelming experience for some people, 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 people, 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, blood sugar testing, medical appointments, daily medications) becomes a "normal" part of the daily routine.

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 below (see 'Where to get more information' below.

Despite the risks associated with type 2 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.

CAUSES

Type 2 diabetes is probably caused by a complex interaction of environmental factors and predisposing genetic factors.

Genetic causes — Many people with type 2 diabetes have a family member with type 2 diabetes or conditions commonly associated with diabetes, such as high cholesterol levels, high blood pressure, or obesity.

The lifetime risk that a first-degree relative (sister, brother, son, daughter) will develop diabetes is five to ten times higher than that of a person with no family history of diabetes.

The likelihood of developing type 2 diabetes is greater in certain ethnic groups; for example, people of Hispanic, African, and Asian descent are at greater risk of developing type 2 diabetes compared to people who are white.

Environmental conditions — Environmental factors such as diet and activity levels interact with genetic causes to influence the development of type 2 diabetes. The incidence of type 2 diabetes has increased dramatically in the United States over the last 20 years as the percentage of people who are obese increases.

Pregnancy — About 3 to 5 percent of pregnant women develop gestational diabetes, usually after 24 to 28 weeks of pregnancy. Gestational diabetes is similar to type 2 diabetes, but generally resolves after a woman delivers her baby. Hormones cause an increase in insulin resistance during pregnancy, which can lead to gestational diabetes. Women who develop gestational diabetes during pregnancy are at high risk for developing type 2 diabetes later in life. (See "Patient information: Gestational diabetes mellitus".)

Other causes — Other, less common causes of diabetes include endocrine conditions that indirectly change the production and action of insulin and lead to diabetes. These include Cushing's syndrome, acromegaly, pheochromocytoma, hyperthyroidism and polycystic ovarian syndrome (PCOS). (See "Patient information: Cushing's syndrome" and "Patient information: Acromegaly" and "Patient information: Hyperthyroidism" and "Patient information: Polycystic ovary syndrome (PCOS)".)

DIAGNOSIS

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

Symptoms — Before being diagnosed with diabetes, some people have symptoms of high blood sugar, including frequent urination, excessive thirst, and blurred vision. Sometimes, diabetes is discovered when a person seeks medical help for another problem (such as erectile dysfunction or pain and numbness in the feet). However, most people with type 2 diabetes have no symptoms at all, and the diagnosis is often delayed for five or more years.

Because family history is a factor in the development of type 2 diabetes, people with family members with diabetes or conditions commonly associated with diabetes, such as hypertension, high blood lipid levels, and obesity, should mention this to their healthcare provider. There are usually few signs of diabetes on a physical examination early in the course of the disease.

Laboratory tests — Several blood tests are used to measure blood glucose levels, 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 the person last ate. A random blood sugar level of 200 mg/dL (11.1 mmol/L) or higher in persons who have symptoms of high blood sugar (see 'Symptoms' above) suggests a diagnosis of diabetes.
• Fasting blood sugar test — Fasting blood sugar testing involves measuring blood sugar after not eating or drinking for 8 to 12 hours (usually overnight). A normal fasting blood sugar level is less than 100 mg/dL (5.55 mmol/L). A fasting blood sugar of 126 mg/dL (7.0 mmol/L) or higher indicates diabetes. The test is done by taking a small sample of blood from a vein or fingertip. It must be repeated on another day to confirm that it remains abnormally high (see 'Criteria for diagnosis' below.
• 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. Normal values for A1C are 4 to 6 percent (table 1). The test is done by taking a small sample of blood from a vein or fingertip.

One expert group has recommended using a hemoglobin A1C test to diagnose diabetes. Unlike other tests, the A1C test can be done at any time of day (before or after eating).

• Oral glucose tolerance test — Oral glucose tolerance testing (OGTT) can be used to diagnose diabetes and pre-diabetes. However, the OGTT is not routinely recommended because it is inconvenient compared to a fasting blood sugar test.

The standard OGTT includes a fasting blood sugar test. The person then drinks a 75 gram liquid glucose solution (which tastes very sweet, and is usually cola or orange-flavored). Two hours later, a second blood sugar level is measured. In some cases, a blood sugar level is measured at 30 minutes and one hour after drinking the glucose solution.

Criteria for diagnosis — The following criteria are used to define a person's blood sugar levels as normal, suggestive of pre-diabetes (defined as an abnormal blood sugar level which is not high enough to be considered diabetic, but with an increased risk of diabetes in the future), or as diagnostic for diabetes.

Normal — Fasting sugar <100 mg/dL (5.55 mmol/L).

Pre-diabetes — Pre-diabetes can be diagnosed based upon a fasting blood sugar test or an OGTT.

• Impaired fasting glucose is defined as a fasting blood sugar level between 100 and 125 mg/dL (5.6 to 6.9 mmol/L).
• Impaired glucose tolerance is defined as a blood sugar level of 140 to 199 mg/dL, measured two hours after a 75 gram oral glucose tolerance test.

At least 50 percent of people with impaired glucose tolerance eventually develop type 2 diabetes, and they have an increased risk of heart disease even if diabetes does not develop. Impaired glucose tolerance is very common; about 11 percent of all people between the ages of 20 and 74 years have impaired glucose tolerance.

Diabetes mellitus — A person is considered to be diabetic if he or she has one or more of the following criteria:

• - Symptoms of diabetes (see 'Symptoms' above) and a random blood sugar of 200 mg/dL (11.1 mmol/L) or higher
• - A fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher
• - A blood sugar of 200 mg/dL (11.1 mmol/L) or higher two hours after a 75 gram oral glucose tolerance test.

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 person has type 1 or type 2 diabetes, based upon the person's need for insulin (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 characteristics such as older age and higher weight suggest, but do not prove, type 2 diabetes.

However, there are situations where it is less clear if a person has type 1 or 2 diabetes. In this situation, additional blood testing may be needed. When the type of diabetes is in doubt, the clinician will usually treat the patient with insulin, as if they have type 1, since it is critical to avoid a potentially dangerous condition known as diabetic ketoacidosis (DKA). People with type 2 diabetes do not usually develop DKA. (See "Patient information: Diabetes mellitus type 1: Overview".)

TREATMENT

A full discussion of the treatment for type 2 diabetes is available separately. (See "Patient information: Diabetes mellitus type 2: Treatment" and "Patient information: Diabetes mellitus type 2: Insulin treatment".)

COMPLICATIONS

Complications of type 2 diabetes may be related to the disease itself or to the treatments necessary to manage diabetes. (See "Patient information: Preventing complications in diabetes mellitus".)

PREGNANCY AND DIABETES

Women with type 2 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 2: Alcohol, exercise, and medical care
Patient information: Foot care in diabetes mellitus
Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus
Patient information: Preventing complications in diabetes mellitus
Patient information: Self-blood glucose monitoring in diabetes mellitus
Patient information: Diabetes mellitus type 2: Treatment
Patient information: Diabetes mellitus type 2: Insulin treatment
Patient information: Type 2 diabetes mellitus and diet
Patient information: Gestational diabetes mellitus
Patient information: Cushing's syndrome
Patient information: Acromegaly
Patient information: Hyperthyroidism
Patient information: Polycystic ovary syndrome (PCOS)
Patient information: Diabetes mellitus type 1: Overview
Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus

Professional Level Information:
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
Glycemic control and vascular complications in type 2 diabetes mellitus
Insulin therapy in type 2 diabetes mellitus
Management of hypoglycemia during treatment of diabetes mellitus
Management of persistent hyperglycemia in type 2 diabetes mellitus
Nutritional considerations in type 1 diabetes mellitus
Nutritional considerations in type 2 diabetes mellitus
Prediction and prevention of type 2 diabetes mellitus
Screening for diabetes mellitus
Smoking and cardiovascular risk in diabetes mellitus
The metabolic syndrome (insulin resistance syndrome or syndrome X)
Treatment of diabetes mellitus in elderly adults
Patient information: Foot care 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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