comparative study of free thyroxine estimation using coat-A-coount ft4 and clinical assays tm ft4

ABSTRACT

To compare the performance characteristics of Diagnostic product corporation [DPC] Coat-A-Count FT 4 single-step radioimmunoassay and Clinical Assays[tm] FT 4 two-step radioimmunoassay procedure in terms of sensitivity, precision, dilution effect and reproducibility using clinical samples. DPC Coat-A- Count Clinical Assays[tm] were used for free thyroxine estimation. All procedures were carried out according to the manufacturers' instructions and in duplicate. 144 blood samples were collected from patients with various conditions in the Pathology Department at King Hussein Medical Center, and the serum stored at-20°C prior to analysis. Linear regression analysis of the results obtained by both methods for 144 patients with various thyroid conditions showed correlation [r=0.98; slope=0.968]. The sensitivity defined as two standard deviation [2SD] below the mean of the zero standard was 0.128 pmol/l for Coat-A-Count FT4 and 0.95 pmol/l for Clinical Assays[tm] FT4. Precision was assessed using human serum samples at low, normal and high FT4 concentration. Intra-run coefficient of variation CV was 4.17% - 8.74% for Coat-A-Count FT4 and 5.37% - 9.76% for Clinical Assays[tm] FT4. Inter-run CV was 6.74% - 11.8% for Coat-A-Count FT4 and 5.7% - 10.69% for Clinical Assays[tm] FT4. The accuracy which is related to a true free hormone in diluted sample was tested. The Coat-A-Count FT4 showed a clear dependence of FT4 estimation on serum concentration [range 100% - 12.5%], while the FT4 estimated by Clinical Assays[tm] FT4 two-step procedure was unaffected. Both assays demonstrated good agreement across a wide range of FT 4 values. Both assays failed to give a clear view concerning thyroid status in nonthyroidal illness patients [chronic renal failure]. Additionally, Coat-A-Count failed the sample dilution test