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Laboratory and clinical experience with a monoclonal antibody-based radioimmunoassay for serum total thyroxine
The performance characteristics and diagnostic value of a monoclonal antibody-based radioimmunoassay for serum total thyroxine (Mallinckrodt) are described. Between-batch precision (coefficient of variation) was 10.4% at 87 nmol/l and 3.3% at 185 nmol/l. Scatchard analysis revealed a linear plot with a Ka of 5.4 X 10(8) l/mol. Sensitivity was 4.5 nmol/l of thyroxine. An association study showed that the assay reached equilibrium well within the specified incubation time. Cross-reaction of triiodothyronine and reverse triiodothyronine in the assay was 0.6% and 25.0% respectively. Analytical recovery was 91-110%. Linearity was well demonstrated but dilutions of a high concentration of thyroxine in serum did not parallel the standard curve. The correlation coefficient for comparison with a polyclonal antibody assay was 0.95 for 83 patients. The diagnostic accuracy of the monoclonal antibody assay was adequate for most patients with thyroid disease, pregnant women, oral contraceptive users and subjects on thyroxine-replacement therapy. Measurement of total thyroxine by a monoclonal antibody-based method shows no definite advantage over the conventional polyclonal antibody assay.
The performance characteristics and diagnostic value of a monoclonal antibody-based radioimmunoassay for serum total thyroxine (Mallinckrodt) are described. Between-batch precision (coefficient of variation) was 10.4% at 87 nmol/l and 3.3% at 185 nmol/l. Scatchard analysis revealed a linear plot with a Ka of 5.4 X 10(8) l/mol. Sensitivity was 4.5 nmol/l of thyroxine. An association study showed that the assay reached equilibrium well within the specified incubation time. Cross-reaction of triiodothyronine and reverse triiodothyronine in the assay was 0.6% and 25.0% respectively. Analytical recovery was 91-110%. Linearity was well demonstrated but dilutions of a high concentration of thyroxine in serum did not parallel the standard curve. The correlation coefficient for comparison with a polyclonal antibody assay was 0.95 for 83 patients. The diagnostic accuracy of the monoclonal antibody assay was adequate for most patients with thyroid disease, pregnant women, oral contraceptive users and subjects on thyroxine-replacement therapy. Measurement of total thyroxine by a monoclonal antibody-based method shows no definite advantage over the conventional polyclonal antibody assay.