THE MEASUREMENT OF URINARY AMINO-TERMINAL TELOPEPTIDES OF TYPE-I COLLAGEN TO MONITOR BONE-RESORPTION IN PATIENTS WITH PRIMARY HYPERPARATHYROIDISM

This study was carried out in order to evaluate clinical usefulness of cross-linked N-telopeptides (NTx) of type I collagen determination, i n patients with primary hyperparathyroidism. Twenty-six consecutive pa tients (6 males and 20 females, aged 56.3+/-15.0, SD, yrs) with primar y hyperparathyroidism were studied in basal conditions and, ten of the m, after surgical cure of the disease. Cross-linked collagen peptides were measured by enzyme-linked immunosorbent assay and conventional ma rkers of bone turnover according to standard procedures. Bone densitom etry at the lumbar spine and proximal femur was performed using dual-e nergy X-ray absorptiometry. Bone mineral density was also assessed at the junction of the distal and middle third of the radius and at the u ltradistal radius of the non-dominant arm by a dual photon densitomete r. Mean urinary NTx values (194.2+/-121.9 pmoles bone collagen equival ents/mu moles creatinine) were significantly higher (p<0.001) in respe ct to those found in normal subjects. The mean increase of Z score val ues of both serum tartrate resistant acid phosphatase activity (1.4+/- 1.8) and the fasting hydroxyproline/creatinine ratio (1.45+/-2.0) was significantly lower (p<0.02) in respect to that of NTx Z score values (3.3+/-3.3); the latter values were not significantly different than m ean Z score values of serum osteocalcin (4.0+/-3.9), serum alkaline ph osphatase activity (2.6+/-2.6) and urinary calcium/creatinine ratio (3 .2+/-3.3). We found a significant inverse correlation between NTx valu es and both lumbar spine (p<0.01) and ultradistal radius bone mineral density (p<0.05); a modest inverse correlation was also observed betwe en serum tartrate resistant acid phosphatase activity and lumbar spine bone mineral density (p<0.04). Following successful adenoma removal, the percentage decrease of both NTx and hydroxyproline was similar in patients with increased bone turnover rate; major discrepancies were o bserved in patients with normal values of NTx, the telopeptide reducti on being greater than that of hydroxyproline. Finally, in a hypercalce mic patient with metastatic parathyroid cancer, telopeptide excretion was shown to be more sensitive in respect to urinary hydroxyproline wh en evaluating the effects of antiresorptive therapy. Our results seem to indicate that amongst the markers with good sensitivity, NTx is the only one that is inversely related with bone mineral density at two d ifferent skeletal sites. This assay should therefore have a place in b oth the initial screening and medical follow-up of patients with this glandular disorder; in fact, in both situations an increased urinary e xcretion of this marker should warn about the possibility of hidden bo ne loss. (C)1997, Editrice Kurtis.