Performance of solid-state 48 detector gamma counter using solid phase total thyroxin and free thyroxin assays.

Abstract

We evaluated the performance of an automated 48 detector KinetiCount gamma counter using solid phase reagents for total thyroxin (TT4) and free thyroxin (FT4). Interassay coefficients of variations (CV) for both total T4 and free T4 ranged from 5.4% to 13%. Between-method correlation coefficients were 0.9798 for TT4 and 0.8844 for FT4. Detection limits for TT4 and FT4 were 3 micrograms/l and 3 ng/l, respectively. TT4 was linear up to 200 micrograms/l. The recovery of TT4 was between 99 to 101%. A computer-stored standard curve for total T4 was stable over a 6-day period. The 48 counting chambers demonstrated stability over a 45-day period with no significant changes in counting efficiency (p greater than 0.5). Precision between the 48 chambers gave a CV of 1.6%. Crosstalk between chambers was less than 0.3% with count rates up to 80,000 cpm. We conclude that the KinetiCount immunoassay system using solid phase separation technology performs well and is suitable for routine clinical use.