The sugar in your blood, or blood glucose, provides your body with the energy it needs to function properly. Your blood glucose fluctuates in response to the foods you eat. If you are healthy, several hormones keep the amount of glucose in your blood within normal ranges. Your doctor can use several glucose tests to determine whether your blood sugar level is healthy.
Fasting Blood Glucose
The fasting blood glucose test measures the amount of sugar in your blood after a period---usually 9 to 12 hours---without food. A normal fasting blood glucose should fall between 70 and 99 mg/dL. If your fasting blood glucose is between 100 and 125 mg/dL, you have an impaired fasting blood glucose, or pre-diabetes. A fasting blood glucose of 126 mg/dL or higher on more than one test generally indicates diabetes.
Oral Glucose Tolerance Test
An oral glucose tolerance test, or OGTT, measures the amount of glucose in your blood after you drink a solution that contains 75 g of glucose. The OGTT determines how well your body controls glucose levels in your blood. A normal OGTT is less than 140 mg/dL. An OGTT that falls between 140 to 200 mg/dL indicates impaired glucose tolerance or pre-diabetes. An OGTT over 200 mg/dL on more than one test usually indicates diabetes.
Hemoglobin A1C
The hemoglobin A1C test, or HbA1c, is a blood test that your doctor can use either to diagnose diabetes or to monitor how well a diabetic person is controlling blood sugar levels. The results of an HbA1c test represent your average blood sugar over a period of two to three months. The lower your HbA1c, the better controlled your blood sugar.
If you are healthy and not diabetic, your HbA1c will likely fall between 4.5 and 6 percent. An HbA1c of 6.5 percent or more is generally indicative of diabetes. If you already have diabetes, your goal is to keep your HbA1c below 7 percent. As your HbA1c increases, so does your risk of developing diabetic complications.
Considerations
Although abnormal blood sugar levels usually indicate diabetes, other conditions can also interfere with the way your body handles glucose. These conditions include kidney failure, hyperthyroidism, pancreatic cancer, inflammation of the pancreas and acute stress. Certain medications may also cause abnormal blood sugar readings. If your blood glucose tests are abnormal, your doctor will likely recommend further diagnostic testing to determine the underlying cause.
