Urinary pyridinium crosslinks of collagen: specific markers of bone resorption in metabolic bone disease.

The hydroxypyridinium compounds pyridinoline and deoxypyridinoline are specific constituents of mature skeletal collagens. They are released into the circulation and excreted in the urine. Their measurement in urine is a sensitive index of the extent of ongoing bone resorption. Currently, quantification of collagen crosslinks in urine is achieved by chromatographic techniques, but more convenient immunoassays will make these measurements more widely available in the near future. Clinical applications of hydroxypyridinium markers include numerous metabolic bone disorders such as osteoporosis, primary hyperparathyroidism, Paget's disease of bone, and metastatic bone disease. Urinary pyridinium crosslinks of collagen also show great promise as markers of therapeutic efficacy in bone disorders associated with accelerated bone resorption.