For all laboratories, on the fifth date, five serum and five urine specimens were sent to each laboratory in order to assess within-run variability of the marker measurements. Each of the six laboratories used one of two assays for urine NTX measurements and one of two assays for serum BAP measurements. For urine NTX, two laboratories (LabCorp and Specialty) used the Osteomark assay (Inverness Medical Innovations, Waltham,

MA, USA), an ELISA using a monoclonal antibody directed against a urinary pool of collagen cross-links originally derived from a patient with Paget’s disease. Four laboratories (ARUP, Esoterix, Mayo, and CHIR-99021 in vivo Quest) used the Vitros enhanced chemiluminescence (ECi) assay (Ortho-Clinical Diagnostics, Rochester, NY, USA), a fully automated platform using the same antigen. For serum BAP, one laboratory (Specialty) used the Metra BAP enzyme immunoassay (Quidel, San Diego, CA, USA), while five laboratories (ARUP, Quest, Esoterix, Mayo, and LabCorp) used Access Ostase (Beckman Coulter, Fullerton, CA, USA), another enzyme immunoassay. Of note,

Metra BAP was formerly called Alkphase-B. Access Ostase was formerly Hybritech Tandem-MP Ostase, which itself was developed from the monoclonal antibody used for the Hybritech Tandem-R Ostase immunoradiometric assay. The laboratories communicated the results Palmatine by fax to the authors’ institutional www.selleckchem.com/products/torin-2.html clinical laboratory, as is done for routine clinical specimens. Urine NTX values were reported by all labs in whole numbers; BAP values were reported by four of the labs to one tenth of a microgram per liter or unit per liter but by Esoterix and Mayo as whole numbers. Following standard practice, labs corrected urine NTX values for dilution by urinary creatinine analysis and reported results as NTX/creatinine ratios (to be referred to see more simply as NTX in this paper). Means,

SDs, and coefficients of variation (CVs, defined as mean/SD) with 95% confidence intervals (CIs) were calculated [8]. A CV for within-run reproducibility for BAP could not be computed for Esoterix because the reported values were rounded to the nearest microgram per liter and did not vary. Two sensitivity analyses were performed: first, a uniform random variate on the interval [−0.5, 0.5] was added to the BAP values reported by that lab and by Mayo, which also rounded to the nearest microgram per liter. Then, the perturbed results were rounded to the nearest 0.1 μg/L, as reported by the other labs. Second, CVs were computed after rounding reported values from all six labs to the nearest microgram per liter (or, for Metra, the nearest U/L).