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  • Also Known As:
  • Fasting Blood Glucose (FBG)
  • Blood Sugar
  • Fasting Blood Sugar (FBS)
  • Fasting Plasma Glucose (FPG)
  • Formal Name:
  • Blood Glucose (Fasting)|Blood Glucose (Random)
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What Is Glucose?

Glucose is the type of sugar that the cells of the human body use as their main energy source. Your body breaks down the food you eat into glucose and other substances. Your liver stores extra glucose and can produce it at times when you are not eating. The glucose goes into your bloodstream, where a hormone called insulin helps bring glucose into your body’s cells.

Too much glucose in the blood can be a sign of diabetes, a serious medical condition that can cause tissue and organ damage if it is not managed. Diabetes can develop if your body can’t make enough insulin or if your body’s cells have trouble accepting insulin.

Too little glucose in the blood is called hypoglycemia. Hypoglycemia is often caused by diabetes medication, but may also be due to health conditions unrelated to diabetes or to other medications.

The Role of Glucose Testing

There are several different reasons a doctor may recommend glucose testing for you. These include screening, diagnosis, and monitoring.


Screening means using tests to find health problems before those problems cause any symptoms or signs that you or your doctor might notice.

If you are over 40, overweight or obese, or have a heightened risk of developing diabetes, your doctor may order one or more screening glucose tests to find prediabetes or diabetes. People with prediabetes have glucose levels that are higher than normal but not high enough to be diagnosed with diabetes.


Diagnosis is the use of tests and procedures to determine what underlying health condition might be causing noticeable signs and symptoms.

If you have symptoms of diabetes, high blood sugar, or low blood sugar, your doctor may order glucose testing for you. Glucose testing may be accompanied by other blood or urine tests to make an accurate diagnosis.


If you have been diagnosed with diabetes or prediabetes, your doctor may want you to track your blood glucose levels with an at-home glucose testing or monitoring device. Your doctor may also recommend periodic laboratory testing during check-ups to learn how your condition is being managed.

Who should get testing?

Your doctor may include glucose testing in a panel of tests for background health information, such as during an annual examination. Your doctor may also want to screen you for elevated glucose if you are at a higher-than-average risk of diabetes. Risk factors for diabetes include:

  • Being 45 years of age or older
  • Being overweight or obese
  • Heart disease, high blood pressure, or high cholesterol
  • Prediabetes
  • Having family members with diabetes
  • A lack of physical activity
  • African American, Asian, Hispanic, or Native American/American Indian ethnicity
  • Polycystic ovarian syndrome

If you are pregnant, your doctor may order glucose testing to screen for gestational diabetes, a type of diabetes linked to hormone changes during pregnancy. Having gestational diabetes can be harmful to the mother and fetus if left untreated and can increase your risk of developing diabetes later in life.

Your doctor may also recommend glucose testing if you are experiencing symptoms of diabetes, including:

  • Frequent urination
  • Excessive hunger or thirst
  • Tingling or loss of feeling in the hands or feet
  • Blurred vision
  • An abnormal number of infections
  • Unexplained weight loss
  • Feeling very tired
  • Skin that is dry
  • Sores that don’t heal quickly
  • Feeling very tired

Additionally, your doctor may order glucose testing if you have symptoms of low blood sugar or other health conditions.

Glucose testing is also an important part of managing prediabetes and diabetes after they are diagnosed.

Types of Glucose Tests

Several different glucose tests are commonly performed for screening and diagnosis.

  • Fasting plasma glucose test: This test measures the amount of glucose in your blood after you have gone without eating or drinking anything but water for at least 8 hours. This test is usually performed in the morning.
  • Random plasma glucose test: This test also measures the amount of glucose in the blood but may be performed at any time of the day, whether or not you’ve eaten recently. It is often conducted on a sample of blood drawn from a vein in your arm and may be included in a panel of blood tests, such as a comprehensive metabolic panel. People diagnosed with diabetes may also test their glucose throughout the day using a fingerstick blood sample and a special device that provides results at home.
  • Glucose tolerance test: This test measures how much glucose is in your bloodstream after you fast overnight and then drink a sugary drink. A glucose tolerance test typically requires more than one blood draw over the course of several hours.
  • Urine glucose test: Urine glucose testing is often part of routine urinalysis. Urinalysis tests for the presence of many substances in the urine. Urine glucose test results are less accurate than blood glucose testing, but your doctor may order this test if you are not able to have a blood test.
  • Continuous glucose monitoring: A continuous glucose monitor reads glucose levels through a tiny wire implanted just below the skin’s surface. This type of monitoring can show blood glucose trends over time.
  • Hemoglobin A1c: Although the hemoglobin A1c test does not measure glucose directly, it does reflect your average blood glucose levels over the past three months by measuring the amount of hemoglobin that has attached glucose.

Although glucose tests most often use blood or urine samples to test for and monitor diabetes, they can also be performed on samples of cerebrospinal fluid (CSF) or joint fluid. Abnormal levels of glucose in the CSF or synovial fluid can be due to viral, bacterial, or fungal infections and other conditions.

If you have abnormal results on a glucose test, your doctor may want to repeat the test or have you take a different type of glucose test to confirm the results. The type of glucose test your doctor may recommend, how often it’s given, when and where you will receive the test, and whether you will need additional testing will depend on your unique situation.

Getting Glucose Testing

Glucose testing for screening and diagnosis takes place in a doctor’s office, clinic, or laboratory. Plasma glucose testing requires drawing blood from a vein using a small needle. Urinalysis involves collecting a fresh sample of urine in a specimen cup.

Your doctor can explain which tests are the most appropriate for your situation, let you know whether you will need to fast before the test and how much time it will take, and give you additional instructions about preparing for your test.

At-home testing

Screening and diagnostic glucose testing is not done at home. But if you are diagnosed with diabetes, you may have to keep track of your blood glucose level using at-home tests. At-home monitoring allows you and your doctor to understand how well your diabetes is being controlled and can help you make treatment decisions if your glucose levels are too high or too low.

At-home blood glucose testing is most commonly done using a glucose meter. Additionally, your doctor may propose that you use continuous glucose monitoring to measure your blood glucose levels at home.

If you are monitoring your glucose levels at home, you may still need to have your blood glucose tested periodically in a clinical setting. Your doctor can advise you which at-home test or tests are right for you and may be able to suggest specific brands or test kits.

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