RADIOIMMUNOASSAY FOR TRIIODOTHYRONINE
A sensitive and precise radioimmunoassay for measurement of triiodothyronine (T3) in unextracted human serum has been developed by using highly specific antiserum for T3 prepared by immunization of rabbits with T3-human serum albumin conjugate. 8-anilino-1-naphthalene sulfonic acid has been employed in order to inhibit binding of T3 to thyroxine binding globulin. T3-free serum as diluent for standard line has been prepared by incubating pooled human serum with charcoal. Different dose response lines were obtained by utilizing different preparations of charcoal treated human sera in standard portion of the assay. Two different normal ranges of serum T3 levels of 116.7±17.9 (SD) and 133.6 ± 16.6 (SD) ng/100 ml were obtained by two different charcoal treated human sera, utilizing the same samples from 50 normal subjects. Thus it is necessary to determine the normal ranges of the assay for each charcoal treated human serum. Serum T3 levels in 100 normal subjects ranged from 72 ng/100 ml to 158 ng/100 ml with a mean value of 111.0±19.1 ng/100 ml. In 31 hyperthyroid patients serum T3 ranged from 230 ng/100 ml to more than 800 ng/100 ml. In 15 hypothyroid patients serum T3 ranged between 12 ng/100 ml and 63 ng/100 ml. Euthyroid subjects accompanying with hypoproteinemia showed low values.