title: A two-step radioimmunoassay for free triiodothyronine in serum.
abstract: Using a high-affinity solid-phase-bound antibody (Ka = 1.2 X 10(11) L/mol), we have standardized a two-step radioimmunoassay for free triiodothyronine (FT3) in serum, based on immunoextraction. The method was validated by comparison with an equilibrium-dialysis procedure (r = 0.96) involving RIA of T3 in the dialysate standardized with the same antibody and by a commercial (Liso-Phase, International-CIS) method. The two-step RIA could detect as little as 0.2 pg per milliliter. The mean CVs within and between assays were 9% and 12%, respectively. FT3 values measured in 30 normal adults ranged from 1.77 to 4.77 ng/L. Comparison with ratios of total T3 to thyroxin-binding globulin showed good agreement in normal subjects, pregnant women, and hypothyroid and hyperthyroid patients.
mesh_terms: D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood; D007037:Hypothyroidism / Q000097:blood; D007106:Immune Sera; D007202:Indicators and Reagents; D011247:Pregnancy; D011863:Radioimmunoassay / Q000379:methods; D011933:Reagent Kits, Diagnostic; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D007106:Immune Sera; D007202:Indicators and Reagents; D011933:Reagent Kits, Diagnostic; D014284:Triiodothyronine