Interlaboratory and intralaboratory comparison of T 3 -uptake methodology.

Triiodothyron me (T3)-upta ke values in selected human serum pools were compared by use of Abbott’s “Trisorb,” Mallinckrodt Nuclear’s “Res0-Mat,” Curtis Nuclear’s “Tri-lonex,” and a standard procedure. In addition, interlaboratory variation was measured among laboratories using the Abbott and Mallinckrodt procedures. Study of methodological variables indicated that incubation time and temperature affect 13 measurement. The Abbott procedure is most liable to variations caused by either time or temperature changes; the Mallinckrodt and Curtis methods are least liable to variations caused by changes in time and temperature, respectively. Between-run variation for sera with low 13-uptake values was greater than within-run variation as measured by the Abbott, Mallinckrodt, or standard procedure. For sera with high T3-uptake values, between-run variation and within-run variation are similar; with the Curtis method this was true for all serum pools. We and the reference laboratories found the Abbott method to be most sensitive in detecting changes in T3-uptake values of samples in the “hyperthyroid” range.