Reliability of spot samples for assessment of urinary excretion of pyridinoline in patients with rheumatoid arthritis

Objective To determine haw well a spot urine sample of patients with active rheumatoid arthritis (RA) can predict 24-hour urinary pyridinoline and deoxypyridinoline excretion Methods Urine samples of 11 hospitalized RA patients taken an 2 consecutive days at 8 a.m. and 4 p.m. were compared with samples from 24-hour collections (gold standard). High-performance liquid chromatography was used to measure the collagen crosslink concentrations. Results Sampling time was the only significant factor (repeated measurement ANOVA). Significant differences were found between morning and 24-hour samples and between morning and afternoon samples, but not between afternoon and 24-hour samples. Conclusions Samples collected in the afternoon (4 p.m) give the best approximation of 24-hour urinary pyridinoline excretion in patients with active rheumatoid arthritis. In longitudinal studies the sampling rime should be fixed.