Development of immunoassays for type-5 tartrate-resistant acid phosphatase in human serum

Tartrate-resistant acid phosphatase (TRAP) is known as a marker of bone resorption. The purpose of this study was the development of a sensitive and specific immunoassay for TRAP.

We have developed two types of immunoassays, enzyme-linked immunosorbent assay (ELISA) and immunoselective enzyme immunoassay (ISEA) using monoclonal antibodies to recombinant TRAP, for determination of TRAP in human serum. To evaluate assay performance, recovery and dilution tests were performed. Further, we determined serum TRAP levels of patients with secondary hyperparathyroidism at different pH conditions.

The detected ranges of ELISA and ISEA were between 0.08 and 5 microg/l and between 0.063 and 4 U/l. Different concentrations of TRAP added were recovered on average at 98.0% in ELISA and 102.9% in ISEA. In the serial dilution test, serum TRAP levels were on average at 101.6% and 109.6% of the expected values in ELISA and ISEA, respectively. The serum TRAP levels of patients with secondary hyperparathyroidism were significantly higher than those of normal controls in ELISA and ISEA. Similar TRAP levels were obtained in the conditions at pH 5.5 and 6.1 in ISEA.

The present findings suggest that our assay methods are applicable for clinical tests, and strengthen the idea that serum TRAP is useful as a marker for bone resorption.