The five most commonly used intact parathyroid hormone assays are useful for screening but not for diagnosing bone turnover abnormalities in CKD-5 patients

Abstract

Assessment of bone turnover for management of renal osteodystrophy is part of routine care in chronic kidney disease Stage 5 (CKD-5) patients. Measurement of intact parathyroid hormone (iPTH) is the most commonly used surrogate marker for bone turnover in these patients. The current study was conducted to evaluate the predictive value of the five most commonly used iPTH assays for bone turnover. In a cross-sectional study, 84 CKD-5 patients underwent bone biopsy and blood drawings for determination of iPTH and total serum alkaline phosphatase (AP). Histologically, patients presented with a broad range of bone turnover abnormalities as determined by activation frequency and bone formation rate/bone surface. Results of the five iPTH assays in each patient correlated but were significantly different. There were also significant differences between iPTH measurements at the same bone turnover level. Using Kidney Disease Outcome Quality Initiative recommended iPTH ranges, all assays showed comparably poor diagnostic performance. At 80% specificity, cut-off values of the 5 iPTH assays for low bone turnover varied from 165 to 550 pg/ml and for high bone turnover from 404 to 1,003 pg/ml. Sensitivities at these cutoffs remained below acceptable standards. Addition of AP measurements to iPTH did not improve diagnostic accuracy. Precise assessment of bone turnover will require utilization of established and novel bone markers reflecting effects of bone turnover rather than measuring only iPTH or other effectors.