Retinopathy develops at similar glucose levels but higher HbA1c levels in people with black African ancestry compared to white European ancestry: evidence for the need to individualize HbA1c interpretation

Abstract

Aims To examine the association of HbA(1c) and glucose levels with incident diabetic retinopathy according to black African or white European ancestry. Methods In this retrospective cohort study of 202 500 US Veterans with diabetes (2000-2014), measures included HbA(1c), outpatient random serum/plasma glucose, and incident retinopathy [conversion from negative to >= 2 positive evaluations (ICD-9 codes), without a subsequent negative]. Results At baseline, the study population had a mean age of 59.3 years, their mean BMI was 31.9 kg/m(2), HbA(1c) level was 57 mmol/mol (7.4%) and glucose level was 8.8 mmol/l, and 77% were of white European ancestry (white individuals) and 21% of black African ancestry (black individuals). HbA(1c) was 0.3% higher in black vs white individuals (P < 0.001), adjusting for baseline age, sex, BMI, estimated glomerular filtration rate (eGFR), haemoglobin, and average systolic blood pressure and glucose. Over 11 years, incident retinopathy occurred in 9% of black and 7% of white individuals, but black individuals had higher HbA(1c), glucose, and systolic blood pressure (all P < 0.001); adjusted for these factors, incident retinopathy was reduced in black vs white individuals (P < 0.001). The population incidence of retinopathy (7%) was associated with higher mean baseline HbA(1c) in individuals with black vs white ancestry [63 mmol/mol (7.9%) vs 58 mmol/mol (7.5%); P < 0.001)], but with similar baseline glucose levels (9.0 vs 9.0 mmol/l; P = 0.660, all adjusted for baseline age, sex and BMI). Conclusions Since retinopathy occurs at higher HbA(1c) levels in black people for a given level of average plasma glucose, strategies may be needed to individualize the interpretation of HbA(1c) measurements.