Tartrate-resistant acid phophatase isoform 5b (TRAP): a novel serum marker of bone resorption in Haemodialysis patients

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XIX Congress of the European Renal Association, Copenhagen

H.G. Wahl¹, M. Bandorski², D. Bandorski², St. Graf ³, D. Sahlfeld³, J. Bohner¹ and W. Fassbinder³

¹Institut für Laboratoriumsmedizin, ²Medizinische Klinik II, ³Medizinische Klinik III, Klinikum Fulda, Germany

Abstract

Background: Inadequate control of serum phosphorous (P) and calcium (Ca) levels leads to various complications in haemodialysis (HD) patients, including cardiovascular and soft tissue calcification, renal osteodystrophy, and is associated with increased mortality. It has been suggested that serum TRAP may be a useful marker of bone resorption and several enzymatic assays measuring its activity have been published. But in human serum TRAP exists in the two isoforms 5a and 5b with only 5b being specific for osteoclasts. TRAP 5b has been shown to be associated with osteoclastic activity in non-uraemic patients. We therefore investigated whether a novel immunoassay specific for TRAP 5b could be used as a specific marker for activated bone resorption in HD patients.

Methods: Pre-dialysis plasma and serum samples were drawn from 163 HD patients twice with a period of 6 months in between. Statistical analysis was done for 126 patients with a complete set of data (67 men and 59 women, age 66.3 ± 13.0 years, HD treatment 5.0 ± 4.5 years, mean ± SD). The mean level of TRAP 5b was clearly elevated with a broader range of levels of intact parathyroid hormone (iPTH) and normal to slightly elevated levels of Ca, P and Ca x P. There were only small mean changes in Ca, P, Ca x P, iPTH and TRAP 5b levels after six months, but we identified two subgroups with significant changes in TRAP 5b. One group (n=20) showed a significant increase of 2.9 ± 0.4 U/l and the other (n=14) a decrease of 4.8 ± 0.7 U/l. Both groups showed only a small decrease in PTH levels. The group with the decrease in TRAP 5b received 2.7 ± 0.4 g Al(OH)₃/day compared to 0.6 ± 0.3 Al(OH)₃/day in the past six months.

Results: The results suggest that TRAP 5b might be an indicator of bone resorption in a very early stage of renal osteodystrophy.

Conclusion: Therapy of renal osteodystrophy is still a matter of controversy. As direct parameters of bone resorption TRAP 5b and β-CrossLaps might show relevant changes at earlier stages than the conventionally used indirect parameters.