Contribution of calcium, phosphorus and 25-hydroxyvitamin D to the excessive severity of secondary hyperparathyroidism in African-Americans with CKD.

Background: Parathyroid hormone (PTH) levels in African-American (AA) chronic kidney disease (CKD) patients exceed those in patients of other races; mechanisms are unknown.

Methods: We performed a cross-sectional analysis of initial laboratory data collected on 2028 CKD patients (505 AA) from US practices using a laboratory CKD service. Serum calcium (Ca), phosphorus (P), 25-hydroxyvitamin D (25-D) and plasma PTH levels were compared between the two groups.

Results: Mean PTH for AA exceeded PTH for non-AA in Stages 2-5 (P<0.001, all four stages). 25-D levels were higher for non-AA in Stages 1-3 (P<0.001). Serum Ca and P did not differ between groups at any stage. Full adjustment for these variables using multivariable generalized linear modeling did not remove the effect of AA race: AA PTH values exceeded non-AA values in CKD Stages 2-5 (P<0.02, all four stages). Serum Ca, P and 25-D were all inversely correlated with PTH levels irrespective of race, but all factors combined accounted for ∼42% of the variance in PTH.

Conclusions: PTH rises with progressive CKD stage far more in AA than in non-AA patients, and only a moderate component of the rise in PTH is explained by changes in serum Ca, P and 25-D in either group. These findings concur with those from other large CKD cohorts and support the need for further study to determine other factors responsible for this racial difference.