Patients diagnosed by OGTT without elevated HbA1c had similar CV, renal disease risks as those without diabetes
A prospective U.K. study found that patients with diabetes based on an oral glucose tolerance test (OGTT) often did not have a diabetic HbA1c level, and risks of cardiovascular (CV) and kidney disease in these patients were similar to those in the nondiabetic general population.
Diabetes diagnosed on an oral glucose tolerance test (OGTT) may not be present on confirmation testing by HbA1c levels, a recent study found.
Researchers used data from the Whitehall II prospective study in the United Kingdom to evaluate the proportion of OGTT-diagnosed diabetes cases that could be confirmed by HbA1c and to assess the risk for macrovascular and microvascular disease in patients with an OGTT-based diagnosis but nondiagnostic HbA1c values. New diabetes cases diagnosed via OGTT in clinical examinations in 2002 to 2004 and 2007 to 2009 were assessed for HbA1c confirmation (defined as an HbA1c level ≥6.5%) in clinical examinations through 2016. The HbA1c levels of the patients with OGTT-diagnosed diabetes at baseline ranged from 4.1% to 12.8% (mean, 6.4%).
All patients were followed for major cardiovascular events until 2017 and for incident chronic kidney disease (CKD) until their last clinical examination. For analysis of vascular disease risk, patients with new OGTT-diagnosed diabetes, with and without diagnostic HbA1c, and patients with preexisting diabetes were compared to diabetes-free participants. The study results were published Aug. 25 by Circulation.
The study included 5,773 patients (405 with known diabetes, 371 with incident OGTT-diagnosed diabetes, and 4,997 with no diabetes) in the analysis of cardiovascular disease (CVD). In this analysis, 222 patients (59.8%) had diabetes according to OGTT that was confirmed by HbA1c and 149 (40.2%) did not. After adjustment for age, sex, ethnicity, occupation, and prevalent CVD at baseline, the 222 patients with HbA1c-confirmed diabetes and the 405 patients with known diabetes had increased risk of CVD compared with the 4,997 diabetes-free patients (hazard ratios, 1.53 [95% CI, 1.12 to 2.10] and 1.85 [95% CI, 1.50 to 2.28], respectively). The hazard ratio for CVD among the 149 patients with OGTT-diagnosed diabetes but nondiagnostic HbA1c levels was 0.99 (95% CI, 0.68 to 1.43).
For the analysis of CKD, the study included 4,687 patients (276 with known diabetes, 282 with incident OGTT-diagnosed diabetes, and 4,129 with no diabetes). There were 487 CKD cases recorded over 6.6 years of follow-up. Among the patients with incident OGTT-diagnosed diabetes, 175 had the diagnosis confirmed by HbA1c and 107 did not. After adjustment for age, sex, ethnicity, occupation, and prevalent CVD at baseline, hazard ratios for CKD were 1.69 (95% CI, 1.09 to 2.62) in the 175 patients with HbA1c-confirmed diabetes and 1.67 (95% CI, 1.22 to 2.28) in the 276 patients with known diabetes. The hazard ratio for the 107 patients with OGTT-diagnosed diabetes but nondiagnostic HbA1c levels was 1.07 (95% CI, 0.68 to 1.43).
The authors noted that OGTT and HbA1c testing in the Whitehall II study were done at subsequent visits rather than at study entry, that diabetes diagnosis was based on a single OGTT or HbA1c test rather than on repeat testing, and that the study included mostly men, among other limitations. “These findings suggest that pickup of CVD and CKD risk is not harmed but rather improved by the preferential use of HbA1c for the diagnosis of diabetes. Therefore, there appears no need to consider OGTT when HbA1c levels or fasting glucose levels are inconclusive, as stated in recent guidelines,” they wrote. “Fasting glucose tests are needed only in exceptional circumstances when HbA1c results are likely to be unreliable.”