Comment on Hubbard et al. Prediabetes and Risk for Cardiovascular Disease by Hypertension Status in Black Adults: The Jackson Heart Study. Diabetes Care 2019;42:2322–2329

Hubbard et al. (1) recently conducted a study and concluded that prediabetes was not associated with an increased risk for cardiovascular disease (CVD) and all-cause mortality regardless of hypertension status. This study was primarily based on two Chinese studies of prediabetes (2,3), which drew a different conclusion that prediabetes significantly increased the risk of CVD when it was concomitant with hypertension. The introduction of the article by Hubbard et al. states that prediabetes is an intermediate glycemic state between normoglycemia and diabetes, including impaired fasting glucose (IFG), impaired glucose tolerance (IGT) diagnosed through an oral glucose tolerance test (OGTT), and hemoglobin A_1c (HbA_1c) between 5.7% and 6.4% (39 and 46 mmol/mol) (1).

In the two Chinese studies, diagnosis of prediabetes included IFG and IGT, and in one of the two Chinese studies HbA_1c between 5.7% and 6.4% (39 and 46 mmol/mol) was also included. By contrast, in the study by Hubbard et al. prediabetes only included IFG and HbA_1c between 5.7% and 6.4%, neglecting the important diagnosis of IGT. Therefore, the diagnosis of prediabetes in the study by Hubbard et al. was less accurate, and the conclusion may be unpersuasive and does not negate the conclusions of the two Chinese studies. For diabetes screening among the general population, the OGTT is recommended by guidelines (4) when fasting plasma glucose and HbA_1c are inconclusive. In clinical trials, accurately distinguishing between diabetes and prediabetes is thought imperative, so OGTT, as the only method for diagnosis of IGT and isolated postchallenge hyperglycemia (fasting plasma glucose level <7.0 mmol/L and 2-h postchallenge plasma glucose level ≥11.1 mmol/L), is necessary. Previous studies have shown that lifestyle intervention in people with IGT could significantly reduce CVD risk and all-cause mortality (5), indicating that IGT played a considerable role in CVD risk assessment in patients with prediabetes. In the study by Hubbard et al., absence of the OGTT resulted in less rigor in diagnostic criteria, and a large number of people with simple IGT or isolated postchallenge hyperglycemia were regarded as having normal glycemia. This diagnostic defect will narrow the differences between groups with prediabetes and those without, which might be why the study found that prediabetes did not increase the risk for CVD events regardless of hypertension status. Further studies are warranted to clarify the role of hypertension in the risk for CVD in patients with prediabetes.