A blood glucose test measures the amount of
a type of sugar, called glucose, in your blood.
Results are often
ready in 1 to 2 hours. Glucose levels in a blood sample taken from your vein
(called a blood plasma value) may differ a little than glucose levels checked
with a finger stick.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Less than or equal to 100 milligrams per deciliter (mg/dL) (5.6 millimoles per liter, or mmol/L).
2 hours after eating (postprandial):2
Less than 140 mg/dL
(7.8 mmol/L) for people age 50 and younger; less than 150 mg/dL (8.3 mmol/L) for people ages 50–60; less than 160 mg/dL (8.9 mmol/L) for people age 60 and older.
Levels vary depending on when and how much you ate at your last meal. In general: 80–120 mg/dL
(4.4–6.6 mmol/L) before meals or when waking up; 100–140 mg/dL (5.5–7.7 mmol/L) at bedtime.
Many conditions can change your blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation
to your symptoms and past health.
For more information on results from an oral glucose tolerance test or glycohemoglobin A1c test, see:
You may have diabetes. To make a diagnosis of type 2 diabetes, your doctor will use the American Diabetes Association's criteria.
Other conditions that can
cause high blood glucose levels include:
A fasting glucose level below 40 mg/dL (2.2 mmol/L) in women or
below 50 mg/dL (2.8 mmol/L) in men that is accompanied by symptoms of
hypoglycemia may mean you have an insulinoma, a tumor
that produces abnormally high amounts of insulin.
levels also may be caused by:
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Eating or drinking less than 8 hours before a
fasting blood test or less than 2 hours before a
2-hour postprandial test.
- Drinking alcohol.
- Illness or
emotional stress, smoking, and caffeine.
- Taking a medicine, such as birth control pills, medicines
used to treat
high blood pressure, phenytoin (Dilantin), furosemide
(Lasix), triamterene (Dyrenium, Dyazide), hydrochlorothiazide
(Esidrix, Oretic), niacin, propranolol (Inderal), or
corticosteroids (prednisone). Some medicines can cause changes in your test results. Make sure
that your doctor knows about any medicines you take and how often you take