Clinical application of immunoassay for urinary total excretion of deoxypyridinoline in patients with osteoporosis

Abstract

Urinary excretion of pyridinium cross-links is one of the biochemical markers for bone resorption in metabolic bone diseases. Efficacy of immunoassay for deoxypyridinoline (D-pyr) for monitoring effects of antiresorptive therapy was evaluated in 44 women with osteoporosis, including 4 patients with asymptomatic primary hyperparathyroidism. Urinary free forms and protein-bound (conjugated) forms of D-pyr were measured totally by a modified enzyme-liked immunoabsorbent assay (ELISA; PYRILINKS-DTM, Metra Biosystem, Mountain View, CA, USA), which required prehydrolysis of urine samples and adequate acidity adjusted with alkali. There was a close relationship between total excretion of D-pyr measured by reverse-phase high performance liquid chromatography (HPLC) and that measured by ELISA. In 27 patients, the percent change of urinary D-pyr by ELISA following hormone replacement therapy (HRT) was similar to that of urinary total forms of D-pyr using HPLC at the end of the first third, and sixth month. In 8 patients whose series of urine samples were corrected following HRT, the percent change of urinary total excretion of D-pyr by ELISA at the end of the third month was approximately −40%, significantly greater than that of excretion of free forms of D-pyr measured by ELISA (−30%;P<.01). In 16 patients, total urinary D-pyr excretion measured by both methods of HPLC and ELISA decreased by approximately 12% within 4h after a single administration of 20 IU of salmon calcitonin. There were significant differences between percent change of urinary total excretion and that of free forms of D-pyr measured by ELISA (P<.05). We conclude that short-term and subtle change of bone resorption following a single injection of salmon calcitonin, as well as long-term effects of HRT, can be detected by measuring total D-pyr excretion in urine irrespective of assays utilized. A modified assay using ELISA for urinary total D-pyr with an easy procedure provides an informative and cost-beneficial tool in monitoring bone resorption in patients with osteoporosis.