Bone to Total Alkaline Phosphatase Ratios Improve Sensitivity and Specificity of Bone Alkaline Phosphatase Immunoassays

Objectives: Evaluate the ability of two bone alkaline phosphatase (ALPB) immunoassays (Ostase, Hybritech Inc and Alkphase-B, Metra Biosystems) to clinically differentiate between osseous and non-osseous ALP sources. Design and Methods: Specimens from patients with either liver or bone disease (Paget’s disease or metastatic cancer) were analyzed by both methods. Results: There was a good correlation between these two assays. Values for ALPB, whether determined as a concentration by the Ostase assay or as an activity by the Alkphase-B assay, were similar for subjects with liver disease or bone disease. However, total ALP (ALPT) activity was higher in liver disease compared to bone. When ALPB was expressed in relation to ALPT, ratios were significantly greater in subjects with bone disease than in those with liver disease. ALPB/ALPT ratios improved the specificity of the Ostase assay from 52% to 86% and the Alkphase-B assay from 58% to 74%. Conclusions: These two ALPB assays have good analytical performance and their clinical utility can be enhanced by expressing ALPB values in relation to ALPT activity.