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HOW IS TYPE 1 DIABETES DIAGNOSED?

Screening People at Risk for Type 1 Diabetes

Researchers are looking for reliable and inexpensive methods for identifying high-risk people, particularly children, who are most likely to develop diabetes type 1. For example, C-peptide is a small protein that is a natural byproduct of insulin synthesis and is deficient in type 1 diabetes. Repeated measurements of C-peptide are useful in assessing the decline in beta-cell functions and may target people at risk for diabetes who may benefit from experimental preventive therapies.

Testing for Diabetes

Fasting Plasma Glucose. In order to simplify the diagnosis of diabetes, the American Diabetes Association has recommended the sole use of the fasting plasma glucose (FPG) test. 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 diabetes type 2 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 and there is considerable controversy about using it as the sole basis for diagnosing diabetes. Arguments against its sole use are the following:

  • Some experts argue that the 126 mg/dl cut-off causes many people to be diagnosed with diabetes type 2 who are only at very small risk for actual complications.

  • On the other hand, the test may show normal results in many people who are still at risk for diabetes. For example, people who take the test in the afternoon and show normal results may have abnormal (and more accurate) levels if they are tested in the morning.

  • It is it not as useful as the glucose tolerance test for predicting people at high risk for diabetes, heart disease or death, nor is it as useful as the glycated hemoglobin test for identifying people with diabetes at risk for severe complications.

  • Some research indicates that the FPG is not as accurate as the glucose tolerance test for detecting diabetes in specific groups (eg, women with a history of gestational diabetes or certain Asian populations.)

At this time, even if a person has normal FPG levels but still has symptoms of diabetes and a family history or other risk factors, then diabetes should not be ruled out and a glucose tolerance test should also be performed.

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.

  • 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. See Above.)

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.

  • 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.