CIRCULATING TELOPEPTIDE TYPE-I IS A PERIPHERAL MARKER OF THYROID-HORMONE ACTION IN HYPERTHYROIDISM AND DURING LEVOTHYROXINE SUPPRESSIVE THERAPY

The aim of the present investigation was to evaluate the clinical perf ormance of serum carboxy-terminal-1-telopeptide (ICTP), a new marker o f bone resorption, in identifying peripheral overexposure to thyroid h ormones, as compared with serum osteocalcin (OC) and serum sex hormone binding globulin (SHBG). Serum ICTP, SHBG, and OC were assayed by spe cific radioassays in three study groups. Group 1:50 perimenopausal wom en on longterm levothyroxine (LT4) suppressive treatment; group 2: 29 women with untreated hyperthyroidism; group 3: 36 normal euthyroid wom en matched with group 1 patients for age, alcohol, smoking habits, and lifestyle. Serum concentrations of SHBG, ICTP, and OC were markedly i ncreased in hyperthyroid patients, whereas only serum ICTP was slightl y but significantly increased in LT4 treated patients. Serum ICTP had higher diagnostic value for hyperthyroidism when compared with SHBG an d to OC (sensitivity: 100%, 71%, 55%; accuracy: 97%, 88%, and 76%, res pectively). 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 ci rculating ICTP and SHBG, and the correlation with serum OC was of lowe r significance. In conclusion, serum ICTP is a sensitive and reliable marker of peripheral thyroid hormone activity at the bone level; its c linical 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 suc h as perimenopausal women.