Racial Variations in the Markers of Mineral Bone Disorders in CKD Patients in South Africa

Abstract

Introduction: Several studies showed that serum intact parathyroid hormone (PTH), phosphate, and vitamin D levels differ across races. These comparative studies were largely carried out between Caucasians and black Americans. However, little is known of the existence of these associations in an African population with chronic kidney disease (CKD). Methods: This cross-sectional multicenter study involved 293 CKD patients from 3 renal units in Johannesburg, South Africa. Results: The 293 CKD patients (208 blacks, 85 whites) had an overall mean age of 51.1 ± 13.6 years, and black patients were significantly younger than the white patients (48.4 ± 13.6 years vs. 57.1 ± 15.5 years; P < 0.001). Compared with whites, blacks had higher median intact PTH (498 [range: 37–1084] pg/ml vs. 274 [range: 131–595] pg/ml; P = 0.03), alkaline phosphatase (122 [range: 89–192] U/L vs. 103 [range: 74–144] U/L; p = 0.03), and mean 25 OH vitamin D3 (26.8 ± 12.7 ng/ml vs. 22.7 ± 12.2 ng/ml, P = 0.01) levels, whereas their median fibroblast growth factor (FGF) level was 23 (100 [range: 34–639] pg/ml vs. 233 [range: 80–1370] pg/ml; P = 0.002), and their mean serum phosphate (1.3 ± 0.5 vs. 1.5 ± 0.5; P = 0.001) levels were significantly lower. In multivariable analyses, black race was independently associated with increased log PTH (β = 0.488, P = 0.01) and decreased log FGF-23 (β = −0.636, P = 0.02). Similarly, blacks had a 3.08 times higher likelihood (95% confidence interval: 1.51–6.30; P = 0.002) of developing severe hyperparathyroidism than whites. Conclusion: This study highlighted the existence of racial differences in the circulating markers of mineral bone disorders in an African CKD population. Keywords: chronic kidney disease, fibroblast growth factor-23, mineral bone disorder, race