Blood Glucose

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

This test is a direct measurement of the blood glucose level. It is most commonly used in the evaluation of diabetes. It is commonly done, on a regular basis after diagnosis as a means of monitoring disease status and progression and to determine appropriate dose for insulin administration, if required.[1], [2]:

This test is also known as blood sugar, fasting blood sugar, FBS, fasting blood glucose, FBG, fasting plasma glucose, FPG, oral glucose tolerance test, OGTT and GTT.


The regulation of blood glucose is complex. A number of hormones are involved in this regulatory system.

  • Insulin: secreted from the beta islet cells in the pancreas, transports glucose into the cells by increasing the permeability of glucose through the cellular membrane. In addition, insulin stimulates fat, protein, and glycogen synthesis. The sum of insulin activity in the body is to decrease blood glucose levels.
  • Glucagon: acts on the liver to cause glycogen breakdown and thus serves to increase blood glucose levels.
  • Other hormones which elevate glucose: epinephrine, cortisol, and thyroxine which act on the liver

The evaluation of serum glucose levels is also helpful in diagnosing many metabolic diseases and metabolic processes such as:

  • Ability of the beta cells of the pancreas to produce insulin.
  • Peripheral resistance to insulin due to decreased insulin receptors on target cells.
  • Ability of the intestines to absorb glucose.
  • Ability of the liver to accumulate and break down glycogen.
  • The presence of increasing amounts of hormones that directly influence the liver, for example, ACTH, epinephrine, cortisol

Patient Preparation

  • For fasting blood glucose, the patient should fast for at least 8 hours prior to the test. Water is permitted.
  • To prevent starvation which may artificially raise the glucose levels, the patient should not fast longer than 16 hours.
  • Withhold insulin or oral hypoglycemics until after blood is obtained.
  • Factor which can cause increased levels
  • food, many forms of stress (trauma, general anesthesia, infection, burns, myocardial infarction), caffeine, pregnancy due to some degree of glucose intolerance, low hematocrit (<35%).
  • Drugs: antidepressants (tricyclics), beta-adrenergic blocking agents, corticosteroids, IV dextrose infusion, dextrothyroxine, diazoxide, diuretics, epinephrine, estrogens, glucagon, isoniazid, lithium, phenothiazines, phenytoin, salicylates (acute toxicity), and triamterene
  • Factors which can cause decreased levels
  • high hematocrit (>55%), capillary measurements from cyanotic areas
  • Drugs: alcohol, insulin, propranolol, oral hypoglycemic drugs (sulfonylureas, tolbutamide, metformin)

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 65-115mg/dL 3.61-6.38mmol/L
Optimal Range 80-100mg/dL 4.44-5.55mmol/L
Alarm Ranges <50 or >250mg/dL <2.78 or >13.88mmol/L

High levels indicate:

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain