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glucose test measures the amount of a type of sugar, called glucose, in your
blood. Glucose comes from
carbohydrate foods. It is the main source of energy
used by the body.
Insulin is a
hormone that helps your body's cells use the glucose.
Insulin is produced in the
pancreas and released into the blood when the amount
of glucose in the blood rises.
Normally, your blood glucose levels
increase slightly after you eat. This increase causes your pancreas to release
insulin so that your blood glucose levels do not get too high. Blood glucose
levels that remain high over time can damage your eyes, kidneys, nerves, and
There are several different types of blood glucose tests.
To make a diagnosis of type 2 diabetes, your doctor will use the American Diabetes Association's criteria.
Blood glucose tests are done to:
For a fasting blood
sugar test, do not eat or drink anything other than water for at least 8 hours
before the blood sample is taken.
If you have diabetes, you may be
asked to wait until you have had your blood tested before taking your morning
dose of insulin or diabetes medicine.
2-hour postprandial test, start eating a meal exactly 2 hours
before the blood sample is taken. A
home blood sugar test is the most common way to check
2-hour postprandial blood sugar levels.
No special preparation is
required before having a random blood sugar or A1c test.
For an oral glucose tolerance test, you'll need to follow a special diet for 3 days before the test. And do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
To learn more about how to prepare for this test, see Oral Glucose Tolerance Test.
Talk to your doctor about any concerns
you have regarding the need for the test, its risks, how it will be done, or
what the results may mean.
To help you understand the importance of this
test, fill out the
medical test information form(What is a PDF document?).
The health professional taking a sample
of your blood will:
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
There is very little risk of a problem from
having blood drawn from a vein.
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:
Reasons you may not be able to
have the test or why the results may not be helpful include:
CitationsAmerican Diabetes Association (2013). Standards of medical care in diabetes—2013. Diabetes Care, 36(Suppl 1): S11–S66.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Other Works ConsultedFischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
July 5, 2011
E. Gregory Thompson, MD - Internal Medicine & Alan C. Dalkin, MD - Endocrinology
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