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Diabetes is largely under-diagnosed, and its prevalence continues to increase by leaps and bounds throughout the United States. Further, about 25% of newly-diagnosed patients already have established diabetic retinopathy and/or microalbuminuria. Several challenges can hinder a timely diagnosis of diabetes. First, the diagnosis is usually based on fasting-plasma glucose (FPG) or an oral glucose tolerance test (OGTT), both of which require patients to fast for 8 to 10 hours before testing is performed. Second, population screening for diabetes in asymptomatic patients is ordinarily recommended by doing questionnaires that evaluate risk without making a definitive diagnosis.

The upshot is that current screening methods for diabetes may fail to identify a significant portion of the population with diabetes. These strategies can also miss patients at high risk for developing the disease. In the July 2008 Journal of Clinical Endocrinology and Metabolism, my colleagues and I published a consensus recommendation suggesting that hemoglobin A1C tests be used as an accepted method for identifying patients with diabetes. The A1C test has long been used as the gold-standard for monitoring established diabetes and could be an effective means for diagnosing diabetes.

Assessing Advantages & Specific Criteria

Unlike the FPG or OGTT, the A1C test does not require patients to fast overnight because it reflects long-term glycemia. Also, FPG and OGTT are affected by relatively short-term changes in diet and exercise, whereas A1C is not. Patients often come to routine doctor visits without fasting, or they may make temporary improvements in diet and exercise in anticipation of their visit, “hiding” what is diabetic-level glycemia in their normal life. The A1C test is a familiar test to clinicians; it’s available, and in fact already used by many clinicians to diagnose diabetes, although not officially accepted as a diagnostic criterion.

In our consensus recommendation, we suggested that A1C measurements of 6.5% or greater should be accepted as a valid criterion for diagnosing diabetes (Table). Levels that are suspicious but less than the diagnostic threshold (a positive screening test) could require further investigation by physicians. In addition to the A1C values, we suggest that a random plasma glucose values in the range of 130mg/dL to 199 mg/dL be regarded as a positive screen, requiring further evaluation. The use of A1C is not without limitations and potential drawbacks. For example, there’s some evidence that there are racial disparities in A1C that are independent of glycemic levels. Hemoglobinopathies can obscure results, depending on the type of assay used. These obstacles, however, are avoidable and our recommendations suggest methods to circumvent or minimize their impact.

Continue Screening Efforts With A1C

The need for patients to fast before testing and the lack of agreed-upon screening criteria for diabetes are serious deficiencies that may contribute to avoidable morbidity and mortality. Screening with A1C testing could help identify some of the millions of Americans who have undiagnosed diabetes. In order to better address the escalating numbers of people with undiagnosed diabetes, efforts are now being made to collect more evidence that could be beneficial for the clinical community.

Christopher Saudek, MD, has indicated to Physician’s Weekly that a conference he spoke at was sponsored by Metrika, Inc.