MKSAP Quiz: Testing for diabetes

This month's quiz asks readers to evaluate a 48-year-old man with an elevated hemoglobin A1c.

A 48-year-old man is evaluated during a routine examination. He has a 6-year history of hypertension treated with amlodipine and atenolol and is currently asymptomatic. His father had a myocardial infarction at age 50 years, and his mother developed type 2 diabetes mellitus at age 64 years.

On physical examination, blood pressure is 138/89 mm Hg, pulse rate is 76/min, and respiration rate is 18/min; BMI is 33. Central obesity is noted, but all other findings are unremarkable.

Results of laboratory studies show a hemoglobin A1c level of 6.6% and a fasting plasma glucose level of 114 mg/dL (6.3 mmol/L).

Which of the following diagnostic tests should be performed next?

A. Oral glucose tolerance test
B. Repeat measurement of fasting plasma glucose level
C. Repeat measurement of hemoglobin A1c value
D. No additional testing

MKSAP Answer and Critique

The correct answer is C. Repeat measurement of hemoglobin A1c value. This item is available to MKSAP 16 subscribers as item 24 in the Endocrinology section. Information about MKSAP 16 is available online.

This patient is at high risk for diabetes mellitus and should have his hemoglobin A1c value remeasured. He has a family history of type 2 diabetes and coronary artery disease, is obese, and has hypertension. According to the American Diabetes Association, in the absence of unequivocal symptomatic hyperglycemia, the diagnosis of diabetes must be confirmed on a subsequent day by repeating the same test suggestive of diabetes (in this patient, the hemoglobin A1c measurement). If results of two different diagnostic tests are available and both are diagnostic for diabetes, additional testing is not needed. Although this patient's hemoglobin A1c value is diagnostic of diabetes, his fasting serum glucose level is only in the range of impaired fasting glucose. Because this patient had two different tests with discordant results, the test that is diagnostic of diabetes (the hemoglobin A1c measurement) should be repeated to confirm the diagnosis.

In this patient without any hyperglycemic symptoms, remeasuring his hemoglobin A1c level is a much simpler and less burdensome way of confirming the diagnosis of diabetes than performing an oral glucose tolerance test.

Because results of measurement of the hemoglobin A1c value and fasting plasma glucose level were discordant, not performing any additional testing is inappropriate.

Key Point

  • If results of two different diagnostic tests for diabetes mellitus are discordant, the test that is diagnostic of diabetes should be repeated.