Glucose, Blood Sugar, Fasting Blood Sugar

This is a test to measure your blood sugar. Glucose is a simple sugar that serves as the main source of energy for the body. The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed by the small intestine, and circulated throughout the body. Most of the body's cells require glucose for energy production; brain and nervous system cells not only rely on glucose for energy, they can only function when glucose levels in the blood remain above a certain level.

The body's use of glucose hinges on the availability of insulin, a hormone produced by the pancreas. Insulin acts as a traffic director, transporting glucose into the body's cells, directing the body to store excess glucose as glycogen (for short-term storage) and/or as triglycerides in fat cells. We can not live without glucose or insulin, and they must be in balance.

Normally, blood glucose levels rise slightly after a meal, and insulin is secreted to lower them, with the amount of insulin released matched up with the size and content of the meal. If blood glucose levels drop too low, such as might occur in between meals or after a strenuous workout, glucagon (another pancreatic hormone) is secreted to tell the liver to turn some glycogen back into glucose, raising the blood glucose levels. If the glucose/insulin feedback mechanism is working properly, the amount of glucose in the blood remains fairly stable. If the balance is disrupted and glucose levels in the blood rise, then the body tries to restore the balance, both by increasing insulin production and by excreting glucose in the urine.

PREPARATION FOR TEST

A blood sample drawn from a vein in your arm or, for a self check, a drop of blood from a skin prick; in general, it may be recommended that you fast before having a blood glucose test; sometimes a random (no preparation) urine sample is used. Your caregiver will instruct you as to what they want prior to your testing.

NORMAL FINDINGS

Normal values depend on many factors. Your lab will provide a range of normal values with your test results. The following information summarizes the meaning of the test results. These are based on the clinical practice recommendations of the American Diabetes Association.

FASTING BLOOD GLUCOSE

  • From 70 to 99 mg/dL (3.9 to 5.5 mmol/L): Normal glucose tolerance

  • From 100 to 125 mg/dL (5.6 to 6.9 mmol/L):Impaired fasting glucose (pre-diabetes)

  • 126 mg/dL (7.0 mmol/L) and above on more than one testing occasion: Diabetes

ORAL GLUCOSE TOLERANCE TEST (OGTT) [EXCEPT PREGNANCY] (2 HOURS AFTER A 75-GRAM GLUCOSE DRINK)

  • Less than 140 mg/dL (7.8 mmol/L): Normal glucose tolerance

  • From 140 to 200 mg/dL (7.8 to 11.1 mmol/L): Impaired glucose tolerance (pre-diabetes)

  • Over 200 mg/dL (11.1 mmol/L) on more than one testing occasion: Diabetes

GESTATIONAL DIABETES SCREENING: GLUCOSE CHALLENGE TEST (1 HOUR AFTER A 50-GRAM GLUCOSE DRINK)

  • Less than 140* mg/dL (7.8 mmol/L): Normal glucose tolerance

  • 140* mg/dL (7.8 mmol/L) and over: Abnormal, needs OGTT (see below)

* Some use a cutoff of More Than 130 mg/dL (7.2 mmol/L) because that identifies 90% of women with gestational diabetes, compared to 80% identified using the threshold of More Than 140 mg/dL (7.8 mmol/L).

GESTATIONAL DIABETES DIAGNOSTIC: OGTT (100-GRAM GLUCOSE DRINK)

  • Fasting*..........................................95 mg/dL (5.3 mmol/L)

  • 1 hour after glucose load*..............180 mg/dL (10.0 mmol/L)

  • 2 hours after glucose load*.............155 mg/dL (8.6 mmol/L)

  • 3 hours after glucose load* **.........140 mg/dL (7.8 mmol/L)

* If two or more values are above the criteria, gestational diabetes is diagnosed.

** A 75-gram glucose load may be used, although this method is not as well validated as the 100-gram OGTT; the 3-hour sample is not drawn if 75 grams is used.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.