Validation of cytochemical section bioassay for thyroid-stimulating immunoglobulins in treated and untreated Graves' disease.

The cytochemical section-bioassay of thyroid stimulating activity is described. Plasma of thyrotoxic patients as well as those on block-replace treatment with carbimazole and thyroid hormones was used. Linear parallel responses were obtained over the range 1.5 X 10(-7) to 1.5 X 10(-5) mU/1 MRC LATS-B standard. The index of precision was 0.19 +/- 0.028. The fiducial limits (p=0.95) of a sample tested on ten separate occasions were 52-192%. Specificity was investigated using time course studies, and the effect of anti-TSH or anti-IgG antisera. No effect of methimazole or a variety of other drugs was detected. The assay is accordingly validated for measurement of TSI in patients both untreated and on block-replace therapy.