Posted Oct 17 , 2017 09:43 AM

Not performing an OGTT results in significant under diagnosis of (pre)diabetes in a high-risk adult Caucasian population

Meijnickman As, et al. International Journal of Obesity 2017_epub 19 July

What were the findings (excerpted from the Abstract)?

Type 2 diabetes (T2DM) is known to be underdiagnosed. Tests for diagnosis include fasting plasma glucose (FPG), oral glucose tolerance test (OGTT) and A1C. A1C can be tested in non-fasting conditions. Therefore, general practitioners almost no longer execute OGTT’s. We evaluated the performance of OGTT versus A1C in a population consisting of overweight and obese subjects, which can be considered a “high risk” population. For this study, 1241 overweight and obese subjects without a history of diabetes (mean age 44y, mean Body Mass Index 38.0 kg/m2) were tested for glucose tolerance status using FPG, OGTT and A1C. In this study, exactly 46.8% were found to have prediabetes and 11.9% were newly diagnosed with T2DM using ADA criteria. Testing only A1C would have resulted in 78 subjects being diagnosed with T2DM, but 47.3% of newly diagnosed patients would have been missed if OGTT would not have been done. Exactly 581 subjects were diagnosed with prediabetes, 1.4% subjects had impaired fasting glucose (IFG), 30.5% had impaired glucose tolerance (IGT), 5.1% subjects had a combined IFG+IGT, and 9.8% had an isolated elevated A1C (5.7-6.4%). Of the 581 subjects with prediabetes, 257 had an A1C <5.7%. Therefore, 44.2% subjects would have been missed when OGTT would not have been done. The authors concluded that in a population with only overweight and obese adult subjects, 46.8% were diagnosed with prediabetes and 11.9% were newly diagnosed with diabetes. Exactly, 5.6% and 20.7% of total population met the diagnostic criteria of the OGTT for diabetes and prediabetes respectively, but did not meet the diagnostic criteria of the A1C. These data suggest that not performing an OGTT results in significant underdiagnose of T2DM in an overweight and obese adult population.

Why is this important?

It is clear from a variety of studies that early detection and treatment of diabetes can reduce complications (J Diabetes Complications. 2017;31(1):94-100), and it is also clear that prevention of diabetes in individuals with prediabetes is both effective and cost effective (Diabetologia. 2017 Aug 2). Thus, the burden should be on the provider to adequately assess the presence of either diabetes or prediabetes. In recent years, there has been a move to use A1C values as cutoffs for the diagnosis of diabetes and prediabetes as they are supposedly good substitutes for OGTTs which had been recommended for years as the gold standard for such decisions. This article is an important reminder that A1C, while useful, may miss significant numbers of individuals at risk for diabetes and when possible patients should have an OGTT performed to more reliably find those individuals who could benefit from early interventions. Do you use only A1C in diagnosis of diabetes or prediabetes? Do you still perform an OGTT to definitively diagnose either condition? What is your experience with OGTT versus A1C?

Read the Abstract: