Clinical assessment of collagen cross-linked N-telopeptides as a marker of bone metabolism in patients with primary hyperparathyroidism

This study assesses the clinical usefulness of collagen cross-linked N- telopeptides (NTx), a new marker for hone resorption, as a marker for primary hyperparathyroidism. The study was conducted on 114 patients who had undergone parathyroidectomy for primary hyperparathyroidism. Urine NTx levels were longitudinally determined by ELISA. Longitudinal serum bone Gla protein (BGP) determinations and dual energy X-ray absorptiometry (DEXA) examinations were also performed before and after parathyroidectomy. Before parathyroidectomy, the mean urine NTx level in primary hyperparathyroidism was 149.0 ± 116.8 pmol BCE/μmol Cr (normal: < 55 pmol BCE/μmol Cr), and the positive rate was 88.5%. The mean BGP level was 33.5 ± 59.1 ng/mL (normal: 12.7 ng/mL), and the positive rate was 77.7%. The NTx positive rate was higher than the BGP positive rate. NTx values were significantly correlated with bone mineral density (P < 0.002) and BGP values (P < 0.005). Two weeks after parathyroidectomy the NTx levels had already decreased significantly to 65.1 pmol BCE/μmol Cr (P < 0.001), and by one month postoperatively they had fallen to 55.9 pmol BCE/μmol Cr, reaching the normal range much sooner than BGP. The NTx normalization rate two weeks postoperatively was 37%, and by 12 months postoperatively it was normal in 83% of patients. BGP levels decreased more gradually than the NTx levels, and only became normal in 9% of cases two weeks postoperatively, as opposed to 74% by 12 months. It is concluded that NTx reflects bone turnover in primary hyperthyroidism, and that it is an excellent marker for bony lesions before and after parathyroidectomy.