RETRACTED ARTICLE:Urinary Cross-linked N-telopeptides of Type I Collagen Levels in Patients with Rheumatoid Arthritis

Osteoclastic activation rather than suppression of bone formation has been suggested to be the dominant process leading to bone loss in rheumatoid arthritis (RA). Although many studies have already shown the correlation of urinary pyridinoline (PYD) and deoxypyridinoline (DPD) levels with RA-related bone loss, urinary cross-linked N-telopeptides of type I collagen (NTx), a more specific marker of bone-derived type I collagen fragments in urine than urinary PYD and DPD in RA, has not been adequately studied. The purpose of the present study was to determine clinical factors that are associated with an increase in urinary NTx levels in patients with RA. One hundred and eighty-four patients with RA and 185 sex- and age-matched controls were enrolled in the study: 71 men, 37–68 years of age (RA: 31, controls: 40); 129 premenopausal women, 30–48 years of age (RA: 67, controls: 62), and 169 postmenopausal women, 48–69 years of age (RA: 86, controls: 83). The correlations of urinary NTx levels, measured by enzyme-linked immunosorbent assay with anatomic grade in the wrist, functional class, duration of disease, steroid use, modified health assessment questionnaire (HAQ) score for the upper and lower extremities, the levels of serum c-reactive protein and rheumatoid factor (RF), erythrocyte sedimentation rate, and/or years since menopause were examined by multiple regression analysis. Urinary NTx levels (nmol BCE/mmol Cr) did not differ significantly between men with RA and controls (53.2 ± 29.6 vs 41.0 ± 19.6, respectively), whereas urinary NTx levels were significantly higher in pre- and postmenopausal women with RA than in respective controls (premenopausal women: 57.1 ± 36.6 vs 42.3 ± 21.3, P <0.01; women: 76.2 ± 27.3 vs 57.1 ± 28.3, P <0.001). In men with RA, no clinical factors were significantly correlated with urinary NTx levels. In premenopausal women with RA, functional class, HAQ score for the upper extremities, and RF were significantly correlated with urinary NTx levels (all P <0.05); in postmenopausal women with RA, functional class and RF were significantly correlated with urinary NTx levels (both P <0.05). These findings suggest that urinary NTx levels were significantly higher only in women with RA than in age-matched controls, and a RA-related increase in urinary NTx levels may be associated with physical inactivity and disease activity.