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Glucose and Diabetes
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Currently under review
Pending specialist review and validation.
A fasting glucose test measures the amount of glucose circulating in your blood after you have not eaten or had calorie-containing drinks for a period of time. It shows how your body maintains blood sugar at rest, without the immediate effects of a recent meal.
This test is performed on a blood sample taken from a vein. It is commonly used with other assessments that look at longer term glucose control or how your body responds to a glucose challenge.
Fasting glucose helps identify problems with how your body uses insulin, such as diabetes or an increased risk of developing diabetes. It is often ordered for routine screening, when you have symptoms that suggest high or low blood sugar, or to monitor known glucose issues.
Understanding your level helps guide lifestyle changes and medication decisions, and informs your risk for heart and kidney disease, nerve problems, and eye complications. It may also be checked before surgery, during hospital care, or when medicines that can affect glucose are started or adjusted.
Your clinician will interpret your result in context, including your age, health history, pregnancy status, symptoms, and medications. One result is only part of the picture, and unexpected findings are often rechecked to confirm.
If your number is higher than expected, your clinician may repeat the test, order a hemoglobin A1c or an oral glucose tolerance test, and discuss steps to reduce risk. If it is lower than expected, your care team will consider diet, activity, alcohol intake, and medicines, and may evaluate for conditions that can cause low blood sugar. You will receive personalized advice about follow-up and when to seek care if symptoms occur.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Not fasting long enough, eating, or drinking beverages with calories before your blood draw can raise the result. Water is fine. Avoid coffee or tea with sugar or cream, and avoid chewing gum or smoking before the test.
Steroids, diuretics, beta agonists, some antipsychotics, and high dose niacin can raise glucose. Insulin and other diabetes medicines can lower it. Tell your clinician about all prescriptions, over the counter drugs, and supplements.
Infections, surgery, pain, poor sleep, or emotional stress can temporarily raise glucose by increasing stress hormones. Severe liver or kidney problems can also affect results.
Strenuous exercise shortly before the test can lower glucose in some people, while inactivity may have the opposite effect. Heavy alcohol use the night before can cause low or high readings.
Hormonal changes in pregnancy can alter glucose regulation. Your clinician may use additional tests during pregnancy to assess for gestational diabetes.
If a blood sample is not processed promptly, cells can consume glucose and lower the measured value. Laboratories use specific tubes and timely processing to limit this effect.
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