ab1901

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

A.C. Verhoeven¹, M. Boers², J.M. te Koppele³, W.H. van der Laan³, J. de Roos³, S. van der Linden¹

¹Internal Medicine/Rheumatology Department, Maastricht University Hospital, Maastricht; ²Clinical Epidemiology Department, University Hospital, ‘de Vrije Universiteit’, Amsterdam; ³Vascular and Connective Tissue Research Division, TNO Prevention & Health, Leiden, The Netherlands.

ABSTRACT
Objective
To determine how 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 on 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 time should be fixed.

Key words
Rheumatoid arthritis, pyridinoline, deoxypyridinoline, collagen crosslinks, urinary excretion, circadian rhythm.

Please address correspondence to: Prof. dr M. Boers, Department of Clinical Epidemiology VE9-78, VU University Hospital, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands.
E-mail: m.boers@azvu.nl
Reprints will not be available from the authors.