Vascular calcification in South African dialysis patients: Ethnic variation, prevalence, detection and haemodynamic correlates

Aim: Studies from the US have shown little effect of ethnicity on vascular calcification in dialysis patients. This has not been examined in the multi-ethnic population of South Africa where genetic and environmental differences may exist. We assessed the extent and severity of vascular calcification in South African dialysis patients according to race and known risk factors. We further evaluated the association of abdominal aorta calcification with coronary artery calcification. Method: Seventy-five CKD-5D patients and 20 healthy controls were enrolled consecutively. All subjects underwent chest computed tomography for coronary calcium score and abdominal X-ray for abdominal aorta calcium score. Ambulatory blood pressure monitoring was generated via radial artery applanation tonometry. Results: Coronary calcification was present in 38.6% of patients and was associated with age and prior cardiovascular disease on multivariate analyses. The median coronary calcium score in black patients was 0 (IQR 0) and 66 in non-Blacks (IQR 383, P < 0.001); controls had a coronary calcium score of 0 (IQR 0). Black race remained a significant negative predictor for coronary calcification after adjustment, prevalence ratio = 0.14 and 95% confidence interval (CI): 0.0-0.53. Vascular calcification was not associated with any ambulatory blood pressure parameter. Using receiver operator characteristic curves, an abdominal aorta calcification score of ≥1 showed an area under the curve of 0.83 to predict a coronary calcium score ≥ 10. Conclusion: Black race appears to protect from vascular calcification in South African CKD-5D patients and this warrants further study regarding the underlying mechanism. The abdominal X-ray is a useful screening tool for coronary calcification. This cross-sectional study of a South African dialysis cohort shows a relatively low prevalence of coronary artery and aortic calcification likely related to the younger age of patients. The main finding though is the significantly lower degree of vascular calcification in black patients compared with whites, which may result from genetic factors. © 2012 Asian Pacific Society of Nephrology.