Assessment of Urinary Pyridinoline Excretion With a Specific Enzyme-Linked Immunosorbent Assay in Normal Adults and in Metabolic Bone Diseases

Pyridinoline (Pyr), a "peeific bone resorption marker, is usually assessed in urim~ by high-performance liquid chromatography (HPLC) aftl~r aeid hydrolysis and a prepurification step. Immunoassays have been developed to measure urinary Pyr directly. Here WI~ developed and evaluated an enzymelinked immunosorbent assay (ELISA), specific for the urinary free Pyr form, in normal adults and in patients with metabolic bone diseases. Urinary Pyr excretion increased significantly with age fUlr men (r = 0.288; P < 0.001) and for women (r = 0.362; p < 0.001). An average 55% increase was noted between premenopausal (n = 41) and early postmenopausal (n = 42) women (mean ± 1 SD; 22.4 ± 6.3 nmol Pyr/mmol creatinine ,md 34.7 ± 16.8 nmol Pyr/mmol creatinine, respectively; p < 0.001). High Pyr levels were found in patients with hyperthyroidism (n = 29; 126.5 ± 84.2 nmol Pyr/mmol creatinine), Pagetʹs disease of bone (n = 30; 61.8 ± 45.8 nmol Pyr/mmol,:reatinine), and primary hyperparathyroidism (n = 10; 57.4 ± 23.9 nmol Pyr/mmol creatinine). In patients with Pagetʹs disease, urinary free Pyr excretion was correlated with urinary hydroxyproline, the conventional bone resorption marker (r = 0.87; P < 0.001), and with total alkaline phosphatase, a marker of bone formation (r = 0.55; P < 0.005). Free Pyr measured by ELISA was highly correlated with total Pyr ~Ind with total deoxypyridinoline HPLC measurements in postmenopausal women (n = 35; r = 0.94 and 0.91, respectively) and in patients with metabolic bone diseases (n = 22; r = 0.91 and 0.88, respectively; p < 0.001). This specific ELISA for free Pyr is a convenient alternative to the HPLC analysis of free Pyr, and could be useful for bone resorption assessment in patients with metabolic bone diseases.