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Confirmation testing for diabetes mellitus

The following laboratory tests are performed to confirm diabetes/prediabetes. There are several different tests available; discuss with your healthcare provider which test is best for you.

Glycated Hemoglobin (Hb) A1C/ A1C 

Normal range: less than 5.7%

Prediabetes range: 5.7%-6.4%

Diabetes range:  6.5% or higher

Fasting Blood Sugar / Fasting Plasma Glucose

Blood sample taken after the person in fasting overnight x 8 hours

Normal Range: below 100mg/dl

Prediabetes Range: 100-125mg/dl

Diabetes Range:  levels greater than 126mg/dl; confirmation testing is done twice, on two separate occasions, especially if the person is asymptomatic. (3)

Two-Hour Oral Glucose Tolerance Test (OGTT)

Plasma glucose levels are measured before and two hours after the ingestion of 75 grams of glucose.

Normal Range: less than 140mg/dl

Prediabetes Range: 140-199 mg/dl

Diabetes confirmation: 200mg/dl or greater.

Diabetes is confirmed with glucose level greater than 200mg/dl.

*Patients should not take any medications that may impact glucose tolerance, such as steroids, thiazide diuretics, statins, and beta blockers.


Random Plasma Glucose Testing (also known as casual glucose testing)

Random glucose testing, in patients experiencing symptoms such as polydipsia, polyphagia and polyuria.

Results plasma glucose levels greater than 200mg/dl are considered sufficient to diagnose diabetes (although many practitioners prefer additional screenings under more controlled circumstances).

For more information on diabetes self management, check with your local branches of the American Diabetes Association at


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