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Diabetes: Type 1


An in-depth report on the causes, diagnosis, and treatment of type 1 diabetes.

Alternative Names

Insulin-dependent Diabetes Mellitus; Juvenile Diabetes


Testing for Glucose Abnormalities

Fasting Plasma Glucose. The fasting plasma glucose (FPG) test is the standard test for diabetes. It is a simple blood test taken after eight hours of fasting. In general, results indicate the following:

  • FPG levels are considered normal up to 110 mg/dl (or 6.1 mmol/L).
  • Levels between 110 and 125 (6.1 to 6.9 mmol/L) are referred to as impaired fasting glucose. They are only slightly above normal but are considered to be risk factors for type 2 diabetes and its complications.
  • Diabetes is diagnosed when FPG levels are 126 mg/dl (7.0 mmol/L) or higher on two different days.

The FPG test is not always reliable, so a repeat test is recommended if the initial test suggests the presence of diabetes, or if the tests are normal in people who have symptoms or risk factors for diabetes. For example, people who take the test in the afternoon and show normal results may actually have abnormal levels that would be revealed if they are tested in the morning.

Glucose Tolerance Test. A glucose tolerance test uses the following procedures:

  • It first employs an FPG test.
  • A blood test is then taken two hours later after drinking a special glucose solution.

The following results suggest different conditions:

  • In people without diabetes, blood sugar increases modestly after drinking the glucose beverage and decreases after two hours.
  • In diabetes, the initial increase is significant and the level remains high, 200 mg/dL (11.1 mmol/L) or more.
  • Measurements that fall between 7.8 and below 11.1 mmol/L put a person at risk for diabetes and are referred to as impaired glucose tolerance . This condition is now strongly associated with a high risk for future diabetes and a higher than average risk for heart disease and poorer survival rates. (Studies suggest it is a much stronger predictor of diabetes than impaired fasting glucose.)
Diagnosis of diabetes
The oral glucose tolerance test is used to diagnose diabetes mellitus. The first portion of the test involves drinking a special glucose solution. Blood is then taken several hours later to test for the level of glucose in the blood. Patients who have diabetes will have higher than normal levels of glucose in their blood.

Test for Glycated Hemoglobin. Another test examines blood levels glycated hemoglobin, also known as hemoglobin A1c (HbA1c). Measuring glycated hemoglobin is not currently used for an initial diagnosis, but it may be useful for determining the severity of diabetes. Some experts think it should be used to help predict complications in people who have FPG levels between 110 and 139, which are above normal but do not indicate full-blown diabetes.

The basis for its use as a diagnostic measurement in diabetes is as follows:

  • Hemoglobin is a protein molecule found in red blood cells. When glucose binds to it, the hemoglobin becomes modified, a process called glycation.
  • Glycation affects a number of proteins, and elevated levels of glycolated hemoglobin is strongly associated with complications of diabetes.
  • A glycated hemoglobin level of 1% above normal range identifies diabetes in 98% of patients. Normal HbA1c levels do not necessarily rule out diabetes, but if diabetes is present and levels are normal, the risk for complications is low.

The test is not affected by food intake so it can be taken at any time. A home test has been developed that might make it easier to measure HbA1c. In general, measurements suggest the following:

  • Normal HbA1c levels should be below 7%.
  • Levels of 11% to 12% glycolated hemoglobin indicate poor control of carbohydrates. High levels are also markers for kidney trouble.

Testing for Insulin Resistance. Investigators hope that some day a simple test for insulin resistance will be available that will be able to identify people at risk for diabetes. Some research suggests that measuring insulin and triglyceride levels during a fasting period may predict a person's sensitivity to insulin.

Autoantibody Tests

Type 1 diabetes is characterized by the presence of a variety of antibodies called autoantibodies that attack the islet cells. These antibodies are referred to as autoantibodies, because they attack the body's own cells -- not a foreign invader. Fingerstick blood tests are now feasible that can test for these autoantibodies, which may be useful in differentiating between type 1 and type 2 diabetes.

Screening Tests for Complications

Screening for Heart Disease. All patients should be tested for hypertension and unhealthy cholesterol and lipid levels and given an electrocardiogram. Other tests may be warranted in patients with signs of heart disease.

Click the icon to see an image of an ECG.

Screening for Kidney Damage and High Blood Pressure. The earliest manifestation of kidney damage is microalbuminuria, in which tiny amounts (30 to 299 mg per day) of protein called albumin are found in the urine. Microalbuminuria is also a marker for other complications involving blood vessel abnormalities, including heart attack and stroke.

Of note, high blood pressure is strongly associated with diabetic nephropathy. In fact, patients with type 2 diabetes who show signs of microalbuminuria typically already have hypertension.

Type 1 diabetes patients with microalbuminuria, on the other hand, usually have normal blood pressure readings in the doctor's office. A 2002 study using home monitors, however, found that in type 1 patients, high systolic blood pressure during sleep often occurs before development of nephropathy. (Systolic pressure is the first and higher number in a blood pressure reading.) Home blood pressure monitoring, then, may help identify type 1 patients at risk for kidney damage.

Screening for Thyroid Abnormalities. Thyroid function tests should be administered.


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