A 2005 study suggested that even people with FPG levels in the high end of the normal range (high 90s) may be at increased risk for developing type 2 diabetes. Obesity further increases this risk. Patients with FPG levels in the upper 90s should strive to exercise and lose weight to help lower their FPG levels.
Glucose Tolerance Test. The oral glucose tolerance test (OGTT) is more complex than the FPG and may overdiagnose diabetes in people who do not have it. Some experts recommend it as a follow-up after FPG, if the latter test results are normal but the patient has symptoms or risk factors of diabetes. The test uses the following procedures:
- It first uses an FPG test.
- A blood test is then taken 2 hours later after drinking a special glucose solution.
The following results suggest different conditions:
- OGTT levels are considered normal up to 140 mg/dL.
- Levels between 140 mg/dL and 199 mg/dL are referred to as impaired glucose tolerance or pre-diabetes.
- Diabetes is diagnosed when OGTT levels are 200 mg/dL or higher.
Both the FPG and OGTT require that the patient not eat for at least 8 hours prior to the test.
Test for Glycated Hemoglobin. Tests for blood levels of glycated hemoglobin, also known as hemoglobin A1c (HbA1c) are not currently used for an initial diagnosis, but they are useful for determining the severity of diabetes. Some experts think this test can 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 glycosylation.
- Glycosylation affects a number of proteins, and elevated levels of glycolated hemoglobin are 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.
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