medwireNews: Failure to conduct an oral glucose tolerance test (OGTT) results in the underdiagnosis of type 2 diabetes, suggests research.
Evaluating the performance of OGTT versus glycated hemoglobin (HbA1c) in 1241 overweight and obese participants, the researchers found that 47% of 148 patients newly diagnosed with type 2 diabetes (according to ADA criteria) and 44% of 581 newly diagnosed with prediabetes met the diagnostic criteria for OGTT but not that for HbA1c.
This corresponded to 6% and 21% of the whole population, respectively, “being wrongfully reassured as having a normal glucose tolerance,” in the absence of OGTT, the researchers highlight.
“These data suggest that not performing an OGTT results in significant underdiagno[sis] of [type 2 diabetes] in an overweight and obese adult population,” they say.
HbA1c has various epidemiologic and methodological advantages over OGTT, and the latter is now rarely used to diagnose diabetes in primary care, say the researchers. However, they stress that “HbA1c and OGTT measurements cannot simply be exchanged – they probably detect and define different categories of dysglycemia.”
The team found that, using OGTT as the gold standard, HbA1c at a cutoff of 5.7% diagnosed prediabetes with a sensitivity of 37% and a specificity of 76% and an area under the receiver operating curve (ROC) of 0.62, where 1.0 indicates perfect discrimination between people with and without prediabetes.
“The relatively low sensitivity and specificity of HbA1c in detecting prediabetes reveals shortcoming of the HbA1c as a screening test which can have devastating consequences, since individuals with prediabetes conditions are known to carry a significant risk of [type 2 diabetes] and cardiovascular comorbidities,” they stress.
Its performance for predicting type 2 diabetes based on a cutoff of 6.5% was good by comparison, they add, with an area under the ROC of 0.81 and a sensitivity and specificity of 53% and 97%, respectively.
Writing in the International Journal of Obesity, researcher Luc Van Gaal (Antwerp University Hospital and University of Antwerp, Belgium) and colleagues note that this study “highlights the limitations of HbA1c in detecting prediabetes and [type 2 diabetes] in overweight and obese subjects.”
In line with guidelines from the European Society of Cardiology and the EASD, they suggest that “it may be wise to implement a multi-step screening model,” whereby HbA1c is tested first and then OGTT subsequently in individuals who do not meet the 6.5% HbA1c cutoff for diabetes but who may still be considered at high risk.
“Screening in this manner is less labor intensive and cost expensive and thus might be good clinical practice by selecting those patients who really need to be tested by OGTT and by avoiding overdiagnosis,” the researchers conclude.
By Catherine Booth
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