BACKGROUND Serum thyroglobulin(Tg) is a valuable and sensitive tool needed in the follow-up of patients with differentiated thyroid cancer(DTC), but antithyroglobulin antibody(Anti-Tg), common in patients with DTC, can interfere with the assay for Tg. In this study, we evaluated the influence of Anti-Tg on the measurement of Tg using the immunoradiometric assay(IRMA). METHODS: In using ELSA-hTg in vivo test(CIS international, Schering, France), a solid phase two-site IRMA was used to measure Tg(23.5ng/mL, 62.5ng/mL) under the absence or presence of three concentrations of Anti-Tg(25U/mL, 50U/mL, 100U/mL). We also performed Tg measurement using patients serum that was mixed with patients serum containing high Anti-Tg. ANOVA and Scheffe tests were performed to evaluate the effect of Anti-Tg on Tg IRMA, and an inverse regression was made to calculate the level of Tg from measured Tg and used Anti-Tg levels and also to assess the degree of effect of anti-Tg on Tg IRMA. RESULTS: In measuring Tg using the standard solution, the presence of Anti-Tg resulted in a falsely suppressed Tg value. The IRMAs for 23.5ng/mL of the standard Tg solution resulted in 24.5+/-.1 ng/mL under no Anti-Tg, 11.8+/-.4ng/mL under 25U/mL of Anti-Tg, 7.7+/-.1ng/mL under 50U/mL of Anti-Tg, and 4.5+/-.4ng/mL under 100U/mL of Anti-Tg. IRMAs 62.5ng/mL of the standard Tg solution resulted in 65.9+/-.7ng/mL under no Anti-Tg, 36.3+/-.2ng/mL under 25U/mL of Anti-Tg, 23.7+/-.7ng/mL under 50U/mL of Anti-Tg, and 14.0+/-.0ng/mL under 100U/mL of Anti-Tg. (ANOVA test, p=0.000). The degree of suppression of the measured Tg value was positively correlated with the Anti-Tg level (Quadratic model regression, Sig T=0.000). The presence of Anti-Tg also resulted in a falsely suppressed Tg value for the Tg measurement using patient's serum. CONCLUSION: The presence of Anti-Tg could consist of the use of Tg as a tumor, therefore Anti-Tg should be measured in all patients diagnosed with DTC. The interpretation of the Tg level must be performed with extreme caution in patients with Anti-Tg.
BACKGROUND Postpartum thyroiditis(PPT) is one of syndromes of thyroid dysfunction that occurs in the first year after parturition. Reported incidence of PPT is 3.9-8.2% of postpartum women in several studies from different countries. The fact that 52-100% of patients with PPT have thyroid autoantibodies, and that lymphocytic infiltration of thyroid gland is the characteristic pathological feature of PPT suggest that PPT is an autoimmune disease. High iodine intake in short term period is known to aggrevate the experimental autoimmune thyroiditis. This study was performed to investigate the incidence and clinical features of PPT in Korean postpartum women who usually ingest excessive amount of idine in immediate postpartum period and to investigate the predictive value of thyroid autoantibodies in the development of PPT in them. METHOD: Between March 1996 and February 1997, 99 women without previous history of any thyroid disease who delivered babies at Boramae hospital were enrolled. Thyroid function parameters(T3, T4, free T4, TSH), thyroid autoantibodies(anti-microsomal antibody, anti-thyroglobulin antibody) and urinary iodine excretion were measured prospectively before and 1, 3 months after delivery. Dietary iodine intake during postpartum period was evaluated by questionnaire, and clinical parameters were followed up. RESULTS: During 3 months of observation, PPT developed in 8.1%(8/99) of postpartum women. Five cases had typical course having thyrotoxic phase and the other 3 cases had hypothyroid phase without toxic phase. However, only one of those required thyroid hormone replacement therapy in the latter group. There were no differences in age, baseline thyroid function parameters, parity, percent cases with family history of thyroid disease between those developed PPT (n=8) and those did not develop PPT(n=91). Duration of high iodine intake(3.8 +- 0.5 wk. vs. 3.7 +- 0.8 wk., p>0.05), total ingested amount of high iodine diet(77 +- 28 vs. 79 +- 24 bowels of miyokguk, p)0.05), and the urinary iodine excretion(1.9 +- 1.4 mg/g creatinine vs. 3.7 +- 3.7mg/g creatinine, p0.05) at 1 month postpartum were not different between two groups. Of 99 total subjects, anti-microsomal antibody(AMA) was present in 13.1%(13/99) before delivery in their sera. Positive predictive value of the presence of AMA before delivery in predicting the development of PPT was 30.8%. CONCLUSION: The fact that incidence of PPT in normal Korean postpartum women who usually have high iodine intake in immediate postpartum period is not higher than those of other countries, and that there was no difference in the amount of iodine intake between those developed PPT and those did not suggest that high iodine intake in immediate postpartum period do not influence on the incidence of PPT. The presence of AMA before delivery had low specificity in prediction of development of PPT, so the measurement of AMA seems not to be a useful screening test.