HbA1c and fasting plasma glucose levels are equally related to incident cardiovascular risk in a high CVD risk population without known diabetes

OBJECTIVES: Type 2 diabetes (T2DM) is associated with increased risk for cardiovascular disease (CVD). Whether screen-detected T2DM, based on fasting plasma glucose (FPG) or on HbA 1c, are associated with different risks of incident CVD in high-risk populations and which one is preferable for diabetes screening in these populations, remains unclear.

METHODS: 8,274 high-risk CVD participants were included from the UCC-SMART cohort. Participants were divided into groups based on prior T2DM diagnosis, and combinations of elevated/non-elevated FPG and HbA 1c (cut-offs at 7 mmol/L and 48 mmol/mol, respectively): Group 0: known T2DM; group 1: elevated FPG/HbA 1c; group 2: elevated FPG, non-elevated HbA 1c; group 3: non-elevated FPG, elevated HbA 1c; group 1 + 2: elevated FPG, regardless of HbA 1c; group 1 + 3: elevated HbA 1c, regardless of FPG; and group 4 (reference), non-elevated FPG/HbA 1c.

RESULTS: During a median follow-up of 6.3 years (IQR 3.3-9.8), 712 cardiovascular events occurred. Compared to the reference (group 4), group 0 was at increased risk (HR 1.40; 95 % CI 1.16-1.68), but group 1 (HR 1.16; 95 % CI 0.62-2.18), 2 (HR 1.18; 95 % CI 0.84-1.67), 3 (HR 0.61; 95 % CI 0.15-2.44), 1 + 2 (HR 1.17; 95 % CI 0.86-1.59) and 1 + 3 (HR 1.01; 95 % CI 0.57-1.79) were not. However, spline interpolation showed a linearly increasing risk with increasing HbA 1c/FPG, but did not allow for identification of other cut-off points.

CONCLUSIONS: Based on current cut-offs, FPG and HbA 1c at screening were equally related to incident CVD in high-risk populations without known T2DM. Hence, neither FPG, nor HbA 1c, is preferential for diabetes screening in this population with respect to risk of incident CVD.