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Tests of Glycemia for the Diagnosis of Type 2 Diabetes Mellitus

R Graham Barr, MD, MPH; David M. Nathan, MD; James B. Meigs, MD, MPH; and Daniel E. Singer, MD
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From Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts; and College of Physicians and Surgeons, Columbia University, New York, New York.

Grant Support: Dr. Barr performed this work while supported by a grant from the U.S. National Institutes of Health (NRSA grant PE-11001).

Requests for Single Reprints: R. Graham Barr, MD, MPH, Division of General Medicine, Columbia–Presbyterian Medical Center, PH-9 East 105, 622 West 168th Street, New York, NY 10032; e-mail, rgb9@columbia.edu.

Current Author Addresses: Dr. Barr: Division of General Medicine, Columbia–Presbyterian Medical Center, PH-9 East 105, 622 West 168th Street, New York, NY 10032.

Dr. Nathan: Diabetes Center, Massachusetts General Hospital, 50 Staniford Street, 3rd floor, Boston, MA 02114.

Drs. Meigs and Singer: General Medicine Division, Massachusetts General Hospital, 50 Staniford Street, 9th Floor, Boston, MA 02114.

Ann Intern Med. 2002;137(4):263-272. doi:10.7326/0003-4819-137-4-200208200-00011
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This paper discusses tests of glycemia for the diagnosis of type 2 diabetes mellitus, with particular reference to the 1997 diagnostic criteria of the American Diabetes Association. The potential benefits of the lower diagnostic threshold for fasting plasma glucose are not well defined. However, the change in the diagnostic cut-off for diabetes mellitus affects as many as 1.9 million persons in the United States; therefore, the medical and social costs of the lower threshold may be considerable.

Type 2 diabetes mellitus is defined by a threshold imposed on the continuous distribution of glycemic levels, typically with respect to risk for microvascular complications. However, the burden of type 2 diabetes relates more to macrovascular than microvascular complications. Because no clear threshold exists for macrovascular complications, a formal balancing of direct and indirect costs with both microvascular and macrovascular complications may be appropriate to establish glycemic thresholds.

Because fasting plasma glucose, hemoglobin A1c, and the oral glucose tolerance test all predict diabetic complications yet test reliability is better for fasting plasma glucose and hemoglobin A1c than for the oral glucose tolerance test, we suggest an alternative diagnostic approach: If random plasma glucose is elevated (≥ 11.1 mmol/L [200 mg/dL]) and the hemoglobin A1c level is more than 2 SDs above the laboratory mean, then diabetes mellitus should be diagnosed, and management should be based on the hemoglobin A1c level. If the result of only one of these tests is positive, then fasting plasma glucose should be tested to evaluate the patient for impaired fasting glucose and diabetes mellitus.

The glycemic threshold for type 2 diabetes should be established by cost-effectiveness analysis. The clinical diagnosis of diabetes mellitus could be streamlined by incorporation of hemoglobin A1c into established criteria.


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Figure 1.
Frequency distributions and prevalence of retinopathy and proteinuria in Pima Indians 35 years of age or older.(40)Left.Middle.Right.1csolid linedashed line

These data are from a report by Knowler and colleagues , in which the study sample was selected without regard to previously diagnosed diabetes or hypoglycemic therapy. Fasting plasma glucose level. Two-hour plasma glucose level on the oral glucose tolerance test. Hemoglobin A levels. For each test, the bars in the top half of the panel show frequencies by intervals that are equally spaced on a logarithmic scale. The smoothed curves represent a mathematical model of two overlapping normal distributions with a common variance, which was fit by maximum likelihood. The left curve for each test represents the distribution in the nondiabetic population; the right curve shows distribution in the separate diabetic population. The antimode for each test is the intersection of these two distributions. The bottom half of the panel shows the prevalence of retinopathy ( ) and proteinuria ( ) in the same participants. To convert glucose levels from mmol/L to mg/dL, divide by 0.05551. Adapted from reference 40 with permission from John Wiley and Sons, Ltd.

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Figure 2.
Prevalence of retinopathy by deciles of the distribution of values on tests for fasting plasma glucose (circles), oral glucose tolerance (squares), and hemoglobin A 1c (triangles).Top.Middle.Bottom.

A cohort of Pima Indians. A sample of Egyptian participants. Participants in the National Health and Nutrition Examination Survey (NHANES) III. Because the prevalence of retinopathy differs among the three study groups, the scales of the axes are not identical. To convert glucose levels from mg/dL to mmol/L, multiply by 0.05551. Adapted from reference 5 with permission from the American Diabetes Association.

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