Diagnosing Diabetes

Abstract

Because almost all populations have a unimodal distribution of glucose concentrations, there are no clear cutpoints to determine a diagnostic level for diabetes. The older criteria (fasting plasma glucose [FPG] concentration ≥140 mg/dL or 2 hour glucose concentration on the oral glucose tolerance test [OGTT] ≥200 mg/dL) were selected because some people whose values exceeded these subsequently developed retinopathy 3 to 8 years later. The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus lowered the FPG concentration criterion to 126 mg/dL to make it equivalent to a 2 hour glucose concentration on the OGTT of 200 mg/dL. Excessive glycation of proteins plays a very important role in the pathogenesis of the microvascular and neuropathic complications of diabetes. 60% of the new cohort of diabetic patients, i.e., those with FPG concentrations of 126 mg/dL through 139 mg/dL will have normal Hb A1C levels and 35% will have values that already meet the American Diabetes Association goal of <7% before any pharmacological therapy is given. Diabetic patients whose Hb A1C levels are maintained below 7% have very little or no development or progression of retinopathy and nephropathy over a 6 to 10 year period. There are potentially negative insurance (life and medical), employment, social and psychological costs associated with the diagnosis of diabetes. Moreover, in the new cohort of diabetic patients, the nonpharmacological treatment is the same whether the patient carries the diagnosis of diabetes or impaired fasting glucose. Therefore, in my view, the FPG concentration criterion for the diagnosis of diabetes should remain ≥140 mg/dL unless patients with lower FPG values have excessive glycation, i.e., Hb A1C levels ≥7% (assuming an upper limit of normal of 6%). This dependence of an elevated Hb A1C level to make the diagnosis of diabetes in patients with FPG concentrations <140 mg/dL is consistent with the older logic of selecting glucose concentrations that were associated with the development of retinopathy. An algorithm for the diagnosis of diabetes utilizing an initial FPG concentration and a subsequent glycated hemoglobin level in selected individuals is suggested. The Endocrinologist 2000; 10: 90-96 Learning Objectives: Be aware of recently recommended changes in the criterion fasting plasma glucose (FPG) for diagnosing diabetes and the significance of the “new cohort” of diabetics that has resulted. Review the association of diabetic complications with elevated levels of FPG and glycosylated hemoglobin (Hb A1C). Consider the clinical practicality of basing management of both the FPG and Hb A1C and what measures are appropriate for “new-cohort” patients.