blood-glucose-test

Why this test may be ordered

• As part of a routine checkup to screen for prediabetes and diabetes
• To help diagnose the cause of symptoms that may mean your blood glucose is too high or too low
• To monitor the side effects of certain long-term medicines that may affect blood glucose

Preparation and collection

If your provider orders a fasting blood glucose test or an oral glucose tolerance test, you will need to fast for at least eight hours before the test. If your glucose test is part of a BMP or CMP test, you may need to fast. Other blood glucose tests don't require any special preparations. Ask your provider whether you need to fast before your glucose test.

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. After an oral glucose tolerance test, you may feel light-headed. Your provider may suggest that you plan to have someone take you home.

Understanding results

The meaning of your test results will depend on which test you had, the results of other tests, and your medical history. Ask your provider what your test results say about your health.

• Higher than normal glucose levels: It may mean you have or are at risk for getting diabetes. Prediabetes and diabetes are the most common causes of high glucose levels, but other possible causes include: an overactive thyroid gland (hyperthyroidism), a problem with your pancreas (including pancreatitis), stress from surgery/very serious illness/trauma, a problem with your adrenal glands (including Cushing's syndrome and pheochromocytoma), or certain medicines. Limitation: This result alone does not confirm a diagnosis. Your provider will interpret it along with other tests and your medical history. Next step: Your provider will discuss what your results mean and whether further testing or follow-up is needed.
• Lower than normal glucose levels (if you have diabetes): If you have diabetes, glucose levels that are lower than normal for you may be caused by: certain diabetes medicines and other medicines that may lower blood glucose, not eating enough (especially after taking diabetes medicine), or being more physically active than usual. Limitation: This result alone does not confirm a diagnosis. Your provider will interpret it along with other tests and your medical history. Next step: Your provider will discuss what your results mean and whether further testing or follow-up is needed.
• Lower than normal glucose levels (if you don't have diabetes): If you don't have diabetes, low blood glucose levels aren't common. If they happen, they may be caused by: liver or kidney disease, underactive adrenal glands (e.g., Addison disease), certain pituitary disorders, an underactive thyroid gland (hypothyroidism), malnutrition, certain medicines, or alcohol use disorder (AUD). Limitation: This result alone does not confirm a diagnosis. Your provider will interpret it along with other tests and your medical history. Next step: Your provider will discuss what your results mean and whether further testing or follow-up is needed.

• The meaning of your test results will depend on which test you had, the results of other tests, and your medical history.
• High or low glucose levels may have multiple possible causes, and this test alone does not diagnose a specific condition.
• There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What to do next

Ask your provider what your test results say about your health. If you have diabetes, you may need to do blood glucose testing at home to help manage your blood glucose levels. Your provider will let you know how often you should test.

• What type of blood glucose test did I have?
• What do my results mean for my health?
• Do I need any follow-up tests or appointments?
• Should I monitor my blood glucose at home?
• What symptoms should I watch for and report?

Evidence source

U.S. National Library of Medicine: blood-glucose-test