Endocrine Abstracts

Objective: Thyroglobulin (Tg) production by normal or malignant thyroidal cells is TSH dependent. The rhTSH administration for Tg stimulation in patients with differentiated thyroid cancer (DTC), after thyroidectomy and eradication of thyroid remnants with I-131, offers an alternative to thyroid hormone withdrawal preventing the progressive morbidity of hypothyroidism. Tg measurement is usually obtained on the 3rd and 5th day after the first rhTSH injection.

Our study’s aim is to evaluate the stimulated Tg on the third and fifth day after rhTSH administration.

Methods: Thirty-three DTC patients (9 men, 24 women) with negative antiTg antibodies and a mean age of 41.2±13.4 years were included. rhTSH was injected twice on two consecutive days. Tg and TSH were measured at baseline and on day 3 and 5 after the first injection. Tg was measured by chemiluminesence (inter assay variation 4%, functional sensitivity 0.9 ng/ml).

Results: At baseline TSH was undetectable up to 0.96 μIU/ml (mean±S.D., 0.21±0.3 μIU/ml) and Tg was also undetectable up to 3.53 ng/ml (0.98±3.4 ng/ml). TSH increased above 65 ng/ml in all patients and was higher on day 3 (mean±SD, 101.8±25.2 ng/ml) than on day 5 (20.2±11.1) compared with baseline (P<0.001), as expected. Tg increased in 7 patients (21.2%), being unchangeable in the rest 26. In these 7 responders mean Tg levels±S.D. were 1.53±1.1 ng/ml at baseline, 8.5±7.7 ng/ml on day 3 and 15.8±21.3 ng/ml on day 5.

Conclusions: In conclusion, after rhTSH injection in differentiated thyroid cancer patients, thyroglobulin measurement only on day 5 is quite enough and seems to be superior than that on day 3.