Thyroid-microsomal antibodies were quantitated by a new technique utilizing tanned sheep red blood cells coated with human thyroid microsomal antigens. This haemagglutination assay (MCHA) correlated with the immunofluorescent antibody (FAB) but not with the thyroglobulin haemagglutination antibodies (TGHA) assay. Of forty-one patients with Hasmimoto's thyroiditis, thirty-nine (95%) were MCHA but only twenty-four (59%) TGHA positive. Titres were similar for the hypothyroid and euthyroid patients. Patients less than 20 years of age had either negative (50%) or low titre (less than 1:160) TGHA but 100% positive MCHA at titres greater than 1:1280. Of twenty-one patients with Graves' disease eighteen (86%) were MCHA and six (29%) TGHA positive. Of thirty-two patients without thyroid disease eleven (34%) were MCHA and/or TGHA positive. On the basis of family history and associated abnormalities, in eight of eleven, positive antibodies may have been due to subclinical Hashimoto's thyroiditis. Fourteen subjects of a control group (10%) were MCHA positive. Seven of ten examined had goitres. MCHA is a simple and quantitative test, useful in the diagnosis of autoimmune thyroid diseases.

Thyroxine by displacement analysis (T4D) along with the resin-T3 (RT3) and resin-T4 (RT4) ratios were determined analytically on serum samples from 160 ‘normal’, 50 hypothyroid and 70 hyperthyroid persons. From these data, the mathematical products of the T4D and either the RT3 or RT4 ratios were calculated and then designated the free thyroxine indices (FTI-T3 and FTI-T4). These were compared to the mean value ± 3 SD range derived from 137 normal blood bank samples. The T4D used alone was the single most accurate diagnostic parameter. The RT3 and RT4 were singularly poor tests for discriminating thyroidal dysfunction from normal. Despite theoretic considerations, the FTI-T4 was superior in diagnostic discrimination compared to the FTI-T3 with 93.8% ‘normal’ but only 16.0% hypothyroid and 0.0% hyperthyroid values in the normal range. The FTI-T4 showed a linear correlation with the free thyroxine concentration obtained by equilibrium dialysis. The FTΓ-T4 is particularly advantageous for clinical use since it is derived from the T4D which obviates interferences from iodine contamination and the RT4 which can be performed in concert with the T4D by a unified procedure.