Diagnostic accuracy of bone turnover markers and bone histology in patients with CKD treated by dialysis

Background The management of chronic kidney disease-mineral and bone disorder requires the assessment of bone turnover, which most often is based on parathyroid hormone (PTH) concentration, the utility of which remains controversial. Study Design Cross-sectional retrospective diagnostic test study. Setting & Participants 492 dialysis patients from Brazil, Portugal, Turkey, and Venezuela with prior bone biopsy and stored (-20°C) serum. Index Tests Samples were analyzed for PTH (intact [iPTH] and whole PTH), bone-specific alkaline phosphatase (bALP), and amino-terminal propeptide of type 1 procollagen (P1NP). Reference Test Bone histomorphometric assessment of turnover (bone formation rate/bone surface [BFR/BS]) and receiver operating characteristic curves for discriminating diagnostic ability. Results The biomarkers iPTH and bALP or combinations thereof allowed discrimination of low from nonlow and high from nonhigh BFR/BS, with an area under the receiver operating characteristic curve > 0.70 but < 0.80. Using iPTH level, the best cutoff to discriminate low from nonlow BFR/BS was <103.8 pg/mL, and to discriminate high from nonhigh BFR/BS was >323.0 pg/mL. The best cutoff for bALP to discriminate low from nonlow BFR/BS was <33.1 U/L, and for high from nonhigh BFR/BS, 42.1 U/L. Using the KDIGO practice guideline PTH values of greater than 2 but less than 9 times the upper limit of normal, sensitivity and specificity of iPTH level to discriminate low from nonlow turnover bone disease were 65.7% and 65.3%, and to discriminate high from nonhigh were 37.0% and 85.8%, respectively. Limitations Cross-sectional design without consideration of therapy. Potential limited generalizability with samples from 4 countries. Conclusions The serum biomarkers iPTH, whole PTH, and bALP were able to discriminate low from nonlow BFR/BS, whereas iPTH and bALP were able to discriminate high from nonhigh BFR/BS. Prospective studies are required to determine whether evaluating trends in biomarker concentrations could guide therapeutic decisions.