title: Microencapsulated antibodies in radioimmunoassay. II. Determination of free thyroxine.
abstract: We describe a method for directly measuring free thyroxine in human serum. Antibody to thyroxine was encapsulated within a semipermeable nylon membrane that excludes substances of relative molecular mass greater than 20,000. The microencapsulated antibody was then presaturated with [125I]thyroxine. Serum incubated with the microcapsules initiated a displacement reaction between free thyroxine and [125I]thyroxine bound to the antibody. The displaced thyroxine was separated from the bound thyroxine by centrifugation and the concentration of free thyroxine determined from a standard curve prepared by use of known amounts of free thyroxine. The within-day coefficient of variation for two control samples was 8.8 and 6.8%; day-to-day precision for the same material was 12.5 and 13.5%. Lipemia, icterus, or hemoglobin had no adverse effect. Interlaboratory evaluation of the procedure revealed no significant difference in mean values for 20 speciments (p greater than 0.05).
mesh_terms: D000906:Antibodies; D003956:Dialysis; D004058:Diffusion; D006454:Hemoglobins; D006801:Humans; D007565:Jaundice / Q000097:blood; D007700:Kinetics; D008567:Membranes, Artificial; D011863:Radioimmunoassay / Q000379:methods*; D013974:Thyroxine / Q000097:blood*; D014280:Triglycerides
chemical_list: D000906:Antibodies; D006454:Hemoglobins; D008567:Membranes, Artificial; D014280:Triglycerides; D013974:Thyroxine