Random Vs. Fasting Blood Glucose Tests

Diabetes is a disease in which levels of glucose, a type of sugar, are abnormally high in the body. Glucose tests can determine if the body is able to store excess glucose. Random tests and fasting tests each have different diagnostic values. A health care provider should review all blood glucose measurements.

Blood Glucose

• Glucose is the primary source of fuel for the body's functions. We get glucose from the breakdown of carbohydrates. After you eat, a complex system in your body maintains blood glucose levels within a range of about 70 milligrams per deciliter (mg/dL) and 130 mg/dL. If the level falls too low, your body releases available stored glucose and fat to compensate. If the blood glucose level climbs too high, the pancreas releases insulin to store the excess glucose in the muscles. In people with glucose intolerance (prediabetes) and diabetes, insulin is either absent or unable to store the excess glucose. This causes damage to blood vessels, leading to the complications seen in some diabetics.

Random Test

• A random blood glucose test is done at any time of the day to measure the blood glucose level at that moment. The American Diabetes Association recommends that blood glucose before a meal not exceed 130 mg/dL, or 180 mg/dL after eating. If your test reveals any levels above this, you should see a health care provider for follow-up and evaluation for glucose intolerance or diabetes. When a provider requests a "fasting blood glucose" test, the laboratory will confirm if this means a random blood glucose test done after at least eight hours of fasting, a glucose test done after fasting that also includes another test two hours after eating, or a glucose tolerance test, where a fasting level is measured before the test begins.

Post Prandial Test

• The two-hour post-prandial test checks blood glucose levels after a meal. A blood sample is taken before a meal and again two hours after the meal. Initial blood glucose levels should be normal, and levels at two hours after eating should be back to normal, below 130 mg/dL.

Hemoglobin A1c

• Hemoglobin is an oxygen-carrying protein in red blood cells. Hemoglobin A1c is a type of hemoglobin that contains glucose. Measuring it gives an accurate picture of blood glucose levels during the previous 90 days. Health care providers request this test to check for compliance in diabetic patients. Hemoglobin A1c should make up no more than 7 percent of the total amount of hemoglobin in your body. Levels above this indicate that a diabetic patient has not been following their treatment protocol properly.

Glucose Tolerance Test

• The glucose tolerance test determines your body's ability to deal with a glucose load. The test consists of taking an initial blood sample when fasting, consuming a glucose load (usually in the form of a soda), and then having blood samples taken each hour for four hours after the glucose load. A normal response is a quick rise in blood glucose after the load with a decrease to normal levels by hour two or three. Increased levels after that time may indicate glucose intolerance or diabetes.

Considerations

• Although home glucose meters are very accurate, the values they provide are no replacement for a health care provider's advice. Always consult with your provider if you get an abnormal blood glucose reading of any kind at any time. Follow your provider's instructions to maintain healthy glucose levels.