1976 Volume 25 Issue 12 Pages 779-785
Since Chopra, et al. produced antibody of triiodothyronine (T3), measurement of serum T3 level by radioimmunoassay has been widely done as a clinical test. However, dextran coated charcoal (DCC) method which is most commonly used for B/F separation requires strict control of incubation temperature and time. The authors improved this disadvantage by using polyethylene glycol (PEG) instead of DCC for B/F separation. Crossreactivities of used antibody with thyroxine, monoiodotyrosine and diiodotyrosine are less than 0.06% which is considered to be satisfactory in comparison with those previously reported.
The recovery ratios of added T3 were between 92.4-105.9% and that reflected T3 concentration well. The dilution test showed good linearity. Correlation of T3 values measured by DCC method and PEG method in 26 sera was good (r=0.99) and linear regression function was y=0.89x+0.30 (y: PEG method and x: DCC method) .
No significant difference were observed in the results obtained by 2 hr incubation at 20-35°C and 24 hr incubation at 4°C. As for the volume of PEG solution, 1.0 ml was most suitable. Samples should be kept at 4°C when centrifugation is impossible within 30 min after addition of PEG.
Also in various conditions of centrifugation, the authors obtained almost same results.
As described above, the authors conquered problem involved in DCC method, and also simplified the assay procedure by using PEG method for B/F separation. PEG method is considered to be a method of choice for clinical routine test for serum T3 levels.
