MARKERS OF BONE TURNOVER IN HYPERTHYROIDISM AND THE EFFECTS OF TREATMENT

Serum osteocalcin (OC) and bone-specific alkaline phosphatase (B-ALP), reflecting bone formation, and urinary pyridinoline cross-link (Pyr) excretion, reflecting bone resorption, have been measured in 27 patien ts with hyperthyroidism and 30 age-matched controls using direct and n ovel immunoassays. Hyperthyroid patients had higher (P < 0.001) levels of all 3 markers compared with control values: Pyr, 246 +/- 181 nmol/ mmol creatinine us. 40 +/- 12 (+515%); OC, 55 +/- 23 vs. 23 +/- 7.4 mu g/L (+139%); and B-ALP, 22 +/- 17 vs. 10.0 +/- 5.0 mu g/L (+120%). OC and Pyr levels were elevated above the normal range in most patients and were significantly correlated with serum free T-3 concentrations ( r = 0.53; P < 0.01 and r = 0.76; P < 0.001; for OC and Pyr, respective ly). B-ALP levels were elevated in 11 of the 27 patients and did not c orrelate with serum thyroid hormone concentrations. After therapy for hyperthyroidism, Pyr and OC levels returned to normal within 1 month, whereas B-ALP transiently increased after 1 month before falling to ba seline levels. The relapse of hyperthyroidism observed in 1 patient wa s associated with a steep increase in bone markers. These results indi cate that Pyr, measured using a new and convenient immunoassay, is a h ighly sensitive marker for altered bone metabolism in hyperthyroidism. The increases in OC and B-ALP were less impressive, suggesting an imb alance between resorption and formation with subsequent rapid bone los s in untreated hyperthyroidism. OC and B-ALP also appear to reflect di fferent aspects of osteoblast metabolism during the treatment of hyper thyroid patients.