Inter-method variability in bone alkaline phosphatase measurement: Clinical impact on the management of dialysis patients

Background: Bone-specific alkaline phosphatase (BAP) is now recommended to assess bone turnover in hemodialysis (HD) patients. However, little is known about potential variability between methods available to measure BAP. Methods: We measured BAP in 76 HD patients with six different assays (Beckman-Coulter Ostase IRMA, Beckman-Coulter Ostase Access, IDS iSYS Ostase, IDS Ostase enzyme immunoassay, DiaSorin Liaison Ostase and Quidel MicroVue BAP). Results: We observed a high correlation between all the assays ranging from 0.9948 (IDS iSYS vs. IDS EIA) to 0.9215 (DiaSorin Liaison vs. Quidel MicroVue). However, using the regression equations, the equivalent concentration of a Beckman-Coulter Access value of 10 g/L can range from 7.7 to 14.4 mu g/L and of 20 mu g/L can range from 16.9 to 27.9 mu g/L with other assays. According to Beckman-Coulter Access, 13%, 50% and 37% of the patients presented BAP values <= 10, between 10 and >= 20 and = 20 mu g/L, respectively. Discrepancies are observed when other assays are used (concordance from 10 to 100%). Conclusions: Analytical problems leading to inter-method variation should be overcome to improve the usefulness of this marker in clinical practice. According to correlation results, recalibration of BAP assays is necessary but should not be a major issue. (C) 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.