Diagnostic Criterion for Diabetes mellitus

Which of the following is a diagnostic criterion for the presence of diabetes mellitus?

A) Random plasma glucose >200 mg per dL
B) Fasting plasma glucose of 140 mg per dL
C) Abnormal glucose tolerance test
D) Hemoglobin A1C (HbA1c) of 7.5
E) All of the above

Answer and Discussion

The answer is E.

American Diabetes Association (ADA) consensus guidelines lowered the blood glucose thresholds for the diagnosis of diabetes. This increased the number of patients diagnosed at an earlier stage, although no studies have demonstrated a reduction in long-term complications.

Blood glucose measurements. The diagnosis of diabetes is based on one of three methods of blood glucose measurement.

• Diabetes can be diagnosed if the patient has a fasting blood glucose level of 126 mg per dL (7.0 mmol per L) or greater on two separate occasions. 
• Diabetes can also be diagnosed with a random blood glucose level of 200 mg per dL (11.1 mmol per L) or greater if classic symptoms of diabetes (e.g., polyuria, polydipsia, weight loss, blurred vision, fatigue) are present.

Lower random blood glucose values (140 to 180 mg per dL have a fairly high specificity of 92% to 98%; therefore, patients with these values should undergo more definitive testing.
A low sensitivity limits the use of random blood glucose testing.

The oral glucose tolerance test is considered a first-line diagnostic test.
In 2003, the ADA lowered the threshold for diagnosis of impaired fasting glucose to include a fasting glucose level between 100 and 125 mg per dL (5.6 and 6.9 mmol per L).

• Impaired glucose tolerance continues to be defined as a blood glucose level between 140 and 199 mg per dL 2 hours after a 75-g load. 

Patients meeting either of these criteria are at significantly higher risk of progression to diabetes and should be counseled on effective strategies to lower their risk, such as weight loss and exercise.

HbA1C. measurement has recently been endorsed by the ADA as a diagnostic and screening tool for diabetes. One advantage of using A1C measurement is the ease of testing because it does not require fasting.

• An HbA1C level of greater than 6.5% on two separate occasions is considered diagnostic of diabetes.