THYROGLOBULIN IS A MORE SENSITIVE INDICATOR OF IODINE DEFICIENCY THANTHYROTROPIN - DEVELOPMENT AND EVALUATION OF DRY BLOOD SPOT ASSAYS FORTHYROTROPIN AND THYROGLOBULIN IN IODINE-DEFICIENT GEOGRAPHICAL AREAS

Immunometric assays were developed for thyrotropin and thyroglobulin u sing time-resolved fluorescence as the measurement signal. The assays were suitable for measurements in serum/plasma or in dry blood spots ( 3 mm diameter). Both assays have acceptable coefficients of variation for dry blood spots (intra-assay median CV < 10%, inter-assay CV < 15% ) in the concentration range of interest (thyrotropin 3 - 250 mU/l, th yroglobulin 10 - 500 mug/l). The relatively high CV values are not onl y due to the assay design but also to the inhomogeneity of the samples used. For serum samples the median intra-assay CV was < 3% for thyrot ropin in the range 0.1 - 50 mU/l and for thyroglobulin between 2 and 5 00 mug/l. The corresponding inter-assay CV were less than 5%. The assa ys were evaluated in field studies carried out under auspices of Inter national Council for Control of Iodine Deficiency Disorders (ICCIDD) w ith the support of UNICEF in Algeria, Peru, India and Zimbabwe, and we re found to be practical inasmuch as dry blood spot samples could be t ransported without special precautions for up to 5 - 6 weeks without s ignificant loss in immunoreactivity. This agrees with other findings. The results showed that serum thyroglobulin levels are a more sensitiv e indicator of iodine deficiency than thyrotropin; elevated thyroglobu lin levels were found in 182/304 children in Zimbabwe compared with el evated thyrotropin level in 28/304 cases. 213/304 children had enlarge d thyroid glands. The cut-off levels used here were 4.5 mU/l thyrotrop in and 20 mug/l for thyroglobulin, both in whole blood. The assays pro ved useful for assessing the efficacy of iodine therapy, either by ora l dosage or intramuscularly (iodised oil). Single oral doses between 1 20 and 960 mg iodine were used, and the single intramuscular dose cont ained 480 mg iodine. Both serum and dry blood spots were analysed. Sin gle oral doses of 480 and 960 mg iodine resulted in normalisation of s erum thyroglobulin levels. The same was true for the 480 mg iodine giv en intramuscularly. Lower single doses did not reduce elevated thyrogl obulin levels to normal values. The assay could also be used to determ ine/confirm athyroidism in newborns, results being available within 6 hours.