blood-glucose-test
Reviewed
Also called: blood sugar, self-monitoring of blood glucose (SMBG), fasting plasma glucose (FPG), fasting blood sugar (FBS), fasting blood glucose (FBG), random blood sugar
A blood glucose test measures the glucose levels in your blood. Glucose is a type of sugar. It is your body's main source of energy.
Specimen: blood
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. 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.
There is very little risk to having a blood test. 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.
What does high blood glucose mean?
Higher than normal glucose levels: If your results show higher than normal glucose levels, it may mean you have or are at risk for getting diabetes. Limitation: Prediabetes and diabetes are the most common causes of high glucose levels. The meaning of your test results will depend on which test you had, the results of other tests, and your medical history. Next step: Ask your provider what your test results say about your health.- 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, being more physically active than usual. Limitation: If you have diabetes, you may need to do blood glucose testing at home to help manage your blood glucose levels. Next step: Your provider will let you know how often you should test.
- Lower than normal glucose levels (if you don't have diabetes): If they happen, they may be caused by: liver or kidney disease, underactive adrenal glands, for example, Addison disease. Limitation: If you don't have diabetes, low blood glucose levels aren't common. Next step: Ask your provider what your test results say about your health.
- 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.
- 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.