The aim of the present investigation was to evaluate the clinical performance of serum carboxy-terminal-1-telopeptide (ICTP), a new marker of
bone resorption, in identifying peripheral overexposure to
thyroid hormones, as compared with serum
osteocalcin (OC) and serum
sex hormone binding globulin (SHBG). Serum ICTP, SHBG, and OC were assayed by specific radioassays in three study groups. Group 1: 50 perimenopausal women on long-term
levothyroxine (LT4) suppressive treatment; group 2: 29 women with untreated
hyperthyroidism; group 3: 36 normal euthyroid women matched with group 1 patients for age, alcohol, smoking habits, and lifestyle. Serum concentrations of SHBG, ICTP, and OC were markedly increased in
hyperthyroid patients, whereas only serum ICTP was slightly but significantly increased in LT4 treated patients. Serum ICTP had higher diagnostic value for
hyperthyroidism when compared with SHBG and to OC (sensitivity: 100%, 71%, 55%; accuracy: 97%, 88%, and 76%, respectively). In group 1, increased serum ICTP was observed in 30 of 50 patients, whereas increased SHBG and OC were found only in 11 of 50 (p < .001). Serum free
thyroid hormone concentrations correlated with circulating ICTP and SHBG, and the correlation with serum OC was of lower significance. In conclusion, serum ICTP is a sensitive and reliable marker of peripheral
thyroid hormone activity at the bone level; its clinical performance is higher than OC and even better than SHBG. Thus, serum ICTP is better than other peripheral markers in monitoring LT4 suppressive
therapy in patients at increased risk for
osteoporosis such as perimenopausal women.