DefinitionA blood sugar test measures the amount of a sugar called glucose in a sample of your blood. Show
Glucose is a major source of energy for most cells of the body, including brain cells. Glucose is a building block for carbohydrates. Carbohydrates are found in fruit, cereal, bread, pasta, and rice. Carbohydrates are quickly turned into glucose in your body. This can raise your blood glucose level. Hormones made in the body help control blood glucose level. Alternative NamesRandom blood sugar; Blood sugar level; Fasting blood sugar; Glucose test; Diabetic screening - blood sugar test; Diabetes - blood sugar test How the Test is PerformedA blood sample is needed. How to Prepare for the TestThe test may be done in the following ways:
How the Test will FeelWhen the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away. Why the Test is PerformedYour doctor may order this test if you have signs of diabetes. More than likely, the doctor will order a fasting blood sugar test. The blood glucose test is also used to monitor people who already have diabetes. The test may also be done if you have:
SCREENING FOR DIABETES This test may also be used to screen a person for diabetes. High blood sugar and diabetes may not cause symptoms in the early stages. A fasting blood sugar test is almost always done to screen for diabetes. If you are over age 45, you should be tested every 3 years. If you're overweight (body mass index, or BMI, of 25 or higher) and have any of the risk factors below, ask your health care provider about getting tested at an earlier age and more often:
Children age 10 and older who are overweight and have at least two of the risk factors listed above should be tested for type 2 diabetes every 3 years, even if they have no symptoms. Normal ResultsIf you had a fasting blood glucose test, a level between 70 and 100 mg/dL (3.9 and 5.6 mmol/L) is considered normal. If you had a random blood glucose test, a normal result depends on when you last ate. Most of the time, the blood glucose level will be 125 mg/dL (6.9 mmol/L) or lower. The examples above show the common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your doctor about the meaning of your specific test results. What Abnormal Results MeanIf you had a fasting blood glucose test:
If you had a random blood glucose test:
Other medical problems can also cause a higher-than-normal blood glucose level, including:
A lower-than-normal blood glucose level (hypoglycemia) may be due to:
Some medicines can raise or lower your blood glucose level. Before having the test, tell your provider about all the medicines you are taking. For some thin young women, a fasting blood sugar level below 70 mg/dL (3.9 mmol/L) may be normal. RisksThere is little risk involved with having your blood taken.Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. Other risks associated with having blood drawn are slight, but may include:
ReferencesAmerican Diabetes Association. 2. Classification and diagnosis of diabetes: standards of medical care in diabetes - 2019. Diabetes Care. 2019;42(Suppl 1):S13-S28. PMID: 30559228 www.ncbi.nlm.nih.gov/pubmed/30559228. Chernecky CC, Berger BJ. Glucose, 2-hour postprandial - serum. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:585. Chernecky CC, Berger BJ. Glucose tolerance test (GTT, OGTT) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:591-593. Why is it important that a patient fast before a urine or blood glucose test?Fasting helps ensure that the blood test records an accurate measure of fasting blood sugar levels. The results help a doctor diagnose or rule out diabetes.
Why is a person told to fast before a blood glucose test?Why Do I Have to Fast? Nutrients in food and drinks go into your bloodstream and can change things measured by the tests, skewing your results. For instance, if you eat or drink before a fasting blood glucose test, your blood sugar probably will be higher than if you hadn't had anything.
Why is fasting glucose test important?The fasting plasma glucose (FPG) test, also known as the fasting blood glucose test (FBG) or fasting blood sugar test, measures the levels of glucose (sugar) in the blood. It is a relatively simple, accurate, and inexpensive test that can screen for diabetes and problems with insulin functioning.
What happens if you don't fast before a blood glucose test?What happens if I don't fast before a blood test? If you don't fast before a test that requires it, the results may not be accurate. If you forget and eat or drink something, call your doctor or lab and ask if the test can still be done. They can then tell you if you need to reschedule your test.
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