[Radioimmunologic determination of plasmatic triiodothyronine. Verification of operative parameters; 1st clinical results].

The experimental determination of the operative parameters of two radioimmunoassay (RIA) systems for the determination of triiodothyronine (T3) level directly in serum is described. The two systems differ both for the agents blocking the aspecific T3-serum protein bindings (sulphonic acid, 8-aniline, 1-Naphtalene in borate buffer: bor-ANS-RIA and Merthiolate in phosphate buffer: PO4-Merth-RIA) and for the methods adopted for compensating the aspecific serum interferences (T3,4 free serum for bor-ANS-RIA and Human Serum Albumine HSA 8% for PO4-Merth-RIA. The tracers are T3-I125 (spec. act. 500 Ci/g for bor-ANS-RIA and 1000 Ci/g for PO4-Merth-RIA). The antisera have been raised in rabbit (T3-bovine SA conjugate for bor-ANS-RIA and T3-HSA conjugate for PO4-Merth-RIA). The incubation conditions are 2degreesC X 24 h for bor-ANS-RIA and room temp. X 2 h for PO4-Merth-RIA. For both systems, the Bound-Free (B-F) separations are carried out by charcoal-dextrane adsorption, 4 mg/tube, 10 min contact. Indicatively, the lowest detection limits of the two systems are about 8 pg T3 for ANS and about 6 pg T3 for Merth. Evidence of parallelism and even superimposition is provided for both assays between the dose-response curve and the serum dilution curve. The calibration curves of the employed antisera are reported (final titres: 1/1000 for ANS and 1/2500 for Merth). 4 different incubation conditions for ANS and 2 for Merth are described and the reasons of choice of the mentioned conditions statistically elucidated. Acceptable statistical comparison between "sample-blank" and the "blank" of the diluents of the employed standard preparations are presented and discussed. F-countings vs. B-countings functions are reported (regression line -- equations: F = 0.93 B + 0.07, n = 15, r = 0.993 for ANS and F = 0.95 B -- 0.02, n = 14, r = 0.992 for Merth) demonstrating the possibility of alternative countings. The recovery regression lines (found f vs. expected e) have equations: f = 1.01 e + 0.08, n = 10, r = 0.999 for ANS and f = 1.08 e -- 1.64, n = 9, r = 0.995 for Merth, implying a practically quantitative recovery in both cases. Thyroxine (T4) cross reaction study has been undertaken under a quite new optics re-calculating the regression lines -- equations of the T3 recovery in the presence of added T4; in that case, the following equations are valid: f = 1.05 e + 0,13, n = 10, r = 0.992 for ANS and f = 1.07 e + 2.26, n = 18, r = 0,985 for Merth. Reducing the maximum added T4 to 1 ng/tube, the cross reaction can be considered as negligible. T3 levels for normal subjects are finally reported: 1.50 +/- 0.80, n= 37 for ANS and 1.40 +/- 0.68, n = 40 for Merth (ng T3/ml, means +/- 2SD).