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Glucose Blood Test

Last updated Nov. 13, 2018

The Glucose Blood Test is used to assess the levels of glucose in blood. It is used to diagnose diabetes, cancers, and other metabolic disorders.


What are the other Names for this Test? (Equivalent Terms)

  • Blood Sugar Blood Test
  • Fasting Blood Glucose Blood Test
  • FPG Blood Test

What is Glucose Blood Test? (Background Information)

  • Glucose is a simple sugar that serves as the fundamental energy source for the body. Some organs, such as the brain, use glucose exclusively for energy
  • Glucose is obtained through the diet, directly and indirectly. Foods may contain glucose; alternatively, more complex sugars, such as maltose, lactose, and starch, are broken down and their components converted into glucose
  • After a meal, blood glucose levels may increase markedly. Conversely, they may fall after a strenuous workout has forced the muscles to use up the body’s glucose stores
  • Blood glucose levels must be maintained in a relatively narrow range. Excess glucose in blood may damage tissues, while deficiencies may cause fatigue, lightheadedness, and brain malfunction
  • The body compensates for the various factors that impact blood glucose levels through the use of hormones. Two such sugar-regulating hormones are insulin and glucagon. They play opposing roles
    • Insulin is made by beta cells of the pancreas. It is released in blood after a rise in blood glucose levels (such as observed after a heavy meal), to help lower it to normal levels. Insulin achieves this by stimulating the cells to ‘take in’ glucose (and other nutrients)
    • Glucagon is made by the alpha cells of the pancreas and has quite the opposite effect. It is released when glucose levels fall below normal (such as after a workout) and causes the cells to produce and release glucose from their stores 
  • Abnormalities or defects in either of these mechanisms may cause abnormalities in blood glucose levels, which can be life-threatening
  • The most common cause of elevated glucose is diabetes mellitus, or just “diabetes”. Diabetes mellitus should not be confused with diabetes insipidus. Diabetes insipidus is a rare disorder whereby the kidneys cannot conserve water
  • There are two types of diabetes mellitus that cause problems with insulin function:
    • Type 1 (or insulin-dependent) diabetes results from the autoimmune destruction of beta cells of the pancreas
    • Type 2 (or insulin-independent) diabetes results from the desensitization of cells to the effects of insulin
    • Apart from the two types, gestational diabetes is a condition that may occur during pregnancy resulting in excessively large babies and exhibiting low glucose levels 
  • The Glucose Blood Test is used to assess the levels of glucose in blood. It is used to diagnose diabetes, cancers, and other metabolic disorders
  • In normal cases, urine should not contain glucose. However, the presence of glucose in urine usually means that excessive levels of glucose has accumulated in blood due to a metabolic disorder

What are the Clinical Indications for performing the Glucose Blood Test?

Following are the clinical indications for performing the Glucose Blood Test:

  • Monitoring glucose levels of individuals with diabetes
  • Screening ‘at risk’ individuals for diabetes
  • Frequent urination
  • Increased thirst
  • Fatigue
  • Blurry vision
  • Rapid weight loss
  • Tingling and numbing in the extremities
  • Giving birth to a baby over 9 pounds
  • Obesity
  • History of cardiovascular disease

How is the Specimen Collected for Glucose Blood Test?

Following is the specimen collection process for Glucose Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected, by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal
  • OR, a finger-stick method (pricking one’s finger) may be used for obtaining a sample of blood

Preparation required: No preparation is required for a random Glucose Blood Test. However, for fasting blood glucose levels, 12-hour fasting is usually recommended. The healthcare provider will recommend the duration of fasting depending on each individual health situation.

What is the Significance of the Glucose Blood Test Result?

The significance of the Glucose Blood Test result is explained:

Increased blood glucose levels may indicate:

  • Diabetes mellitus
  • Acromegaly
  • Cushing’s syndrome
  • Glucagonoma
  • Severe liver disease
  • Pheochromocytoma
  • Pancreatitis

Decreased blood glucose levels may indicate:

  • Addison’s disease
  • Galactosemia
  • Hereditary fructose intolerance
  • Hypopituitarism
  • Insulinoma
  • Malabsorption syndromes
  • von Gierke disease

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

Certain factors may interfere with the results of the Glucose Blood Test. These include:

  • Stress
  • Pregnancy
  • Diet (recent)
  • Exercise

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: May 15, 2015
Last updated: Nov. 13, 2018