Differences in bone turnover and intact PTH levels between African American and Caucasian patients with end-stage renal disease

Background. Evidence derived from healthy subjects suggests that African Americans have higher serum parathyroid hormone (PTH) levels and decreased bone responsiveness to PTH than Caucasians. African American patients with end-stage renal disease (ESRD) also have higher serum PTH than Caucasians. Studies that correlate intact PTH (iPTH) levels with bone turnover in ESRD patients were performed in a predominantly Caucasian population. Methods. In this study, serum iPTH and bone histomorphometric data were analyzed for racial differences in 76 ESRD patients (Caucasian = 48, African Americans = 28). Bone turnover was determined by histomorphometric measurement of activation frequency in all patients. Results. Age, duration of dialysis, and calcium and phosphorus levels were similar between the two groups. iPTH levels (pg/mL; mean +/- SE) were significantly higher in the African American group (534 +/- 79 vs. 270 +/- 46, P < 0.01). Also, alkaline phosphatase levels (IU/L) were significantly higher in the African American group (162 +/- 31 vs. 144 +/- 43, P < 0.01). Correlations between PTH levels and activation frequency were r = 0.60, P < 0.01 in Caucasians and r = 0.22, P = NS in African Americans. The mean PTH level in African American patients with histologic findings of low bone turnover was 460 +/- 115 vs. 168 +/- 41 in Caucasian patients with similar bone turnover (P < 0.01). In patients with low bone turnover, African Americans had significantly higher osteoid volume and thickness, number of osteoblasts and osteoclasts, erosion surface, peritrabecular fibrosis, and single-label surface than Caucasians. However, erosion depth, bone formation rate per osteoblast and mineralization apposition rate were similar between the two groups. Conclusion. There is no correlation between iPTH and bone turnover in African Americans with ESRD. A substantial number of African American patients with low bone turnover have very high serum PTH levels. Bone histomorphometric results reveal differences in remodeling dynamics and responses to PTH between African American and Caucasian patients. Further studies utilizing newer PTH measurement assays are needed to better delineate the correlation between PTH and bone turnover in the various racial groups.