The utility of fasting glucose for detection of prediabetes.

Treatment of prediabetes attenuates progression to type 2 diabetes mellitus. The American Diabetes Association (ADA) previously defined prediabetes as either impaired fasting glucose (IFG) = 6.1 to 6.9 mmol/L (110-125 mg/dL) and/or impaired glucose tolerance (IGT) (2-hour postload glucose of 7.8-11.0 mmol/L [140-199 mg/dL]). For practical reasons, fasting plasma glucose (FPG) is commonly used for diabetes screening. Recently, the ADA lowered the fasting glucose threshold value for IFG from 110 to 100 mg/dL. Our objective was to determine the utility of FPG alone for detecting prediabetes in African Americans. Oral glucose tolerance test (OGTT) data from a cohort of 304 young adult African American men and women were examined. We calculated prediabetes prevalence using the previous ADA criteria and examined the effect of lowering the IFG threshold value for IFG to 100 mg/dL. The prediabetes prevalence in this cohort using the previous ADA criteria was 20.4% (n = 62). Of the 62 cases, 8 had IFG, 45 had IGT, and 9 had IFG together with IGT. Fasting plasma glucose testing alone detected 17 (27.4%) prediabetic cases, whereas a complete OGTT detected 54 (87.1%). Lowering the IFG threshold value to FPG = 100 mg/dL identified 13 of the 45 IGT-only cases. However, this lower IFG threshold increased prediabetes prevalence in the overall cohort from 20.4% to 31.9%. In conclusion, in young adult African Americans, an ethnic group at high risk for developing diabetes, FPG testing alone may be inadequate for diagnosing prediabetes. Until alternative strategies are identified, an OGTT is presently the best method for detecting the prediabetic condition in these high-risk patients.