What is a blood glucose test?
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. A hormone called insulin helps move glucose from your bloodstream into your cells. Too much or too little glucose in the blood can be a sign of a serious medical condition. High blood glucose levels (hyperglycemia) may be a sign of diabetes, a disorder that can cause heart disease, blindness, kidney failure and other complications. Low blood glucose levels (hypoglycemia) can also lead to major health problems, including brain damage, if not treated.
Other names: blood sugar, self-monitoring of blood glucose (SMBG), fasting plasma glucose (FPG), fasting blood sugar (FBS), fasting blood glucose (FBG), glucose challenge test, oral glucose tolerance test (OGTT)
What is it used for?
A blood glucose test is used to find out if your blood sugar levels are in the healthy range. It is often used to help diagnose and monitor diabetes.
Why do I need a blood glucose test?
Your health care provider may order a blood glucose test if you have symptoms of high glucose levels (hyperglycemia) or low glucose levels (hypoglycemia).
Symptoms of high blood glucose levels include:
- Increased thirst
- More frequent urination
- Blurred vision
- Wounds that are slow to heal
Symptoms of low blood glucose levels include:
You may also need a blood glucose test if you have certain risk factors for diabetes. These include:
- Being overweight
- Lack of exercise
- Family member with diabetes
- High blood pressure
- Heart disease
If you are pregnant, you will likely get a blood glucose test between the 24th and 28th week of your pregnancy to check for gestational diabetes. Gestational diabetes is a form of diabetes that happens only during pregnancy.
What happens during a blood 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. For some types of glucose blood tests, you will need to drink a sugary drink before your blood is drawn.
If you have diabetes, your health care provider may recommend a kit to monitor your blood sugar at home. Most kits include a device to prick your finger (lancet). You will use this to collect a drop of blood for testing. There are some newer kits available that don’t require pricking your finger. For more information on at-home test kits, talk to your health care provider.
Will I need to do anything to prepare for the test?
You will probably need to fast (not eat or drink) for eight hours before the test. If you are pregnant and are being checked for gestational diabetes:
- You will drink a sugary liquid one hour before your blood is drawn.
- You won’t need to fast for this test.
- If your results show higher than normal blood glucose levels, you may need another test, which requires fasting.
Talk to your health provider about specific preparations needed for your glucose test.
Are there any risks to the test?
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 do the results mean?
If your results show higher than normal glucose levels, it may mean you have or are at risk for getting diabetes. High glucose levels may also be a sign of:
- Kidney disease
- Pancreatic cancer
If your results show lower than normal glucose levels, it may be a sign of:
- Too much insulin or other diabetes medicine
- Liver disease
If your glucose results are not normal, it doesn’t necessarily mean you have a medical condition needing treatment. High stress and certain medicines can affect glucose levels. To learn what your results mean, talk to your health care provider.
Is there anything else I should know about a blood glucose test?
Many people with diabetes need to check blood glucose levels every day. If you have diabetes, be sure to talk to your health care provider about the best ways to manage your disease.