Enzyme immunometric assay for L-thyroxine using direct ultraviolet irradiation

A new enzyme immunometric assay for L-thyroxine using uv irradiation as a cross-linking procedure is described. L-Thyroxine in plasma samples is immunocaptured by a monoclonal anti-L-thyroxine antibody coated on 96-well microtiter plates. After uv irradiation and methanol treatment, the covalently linked L-thyroxine is measured using the same monoclonal anti-L-thyroxine antibody labeled with acetylcholinesterase. A minimal detectable concentration of 4.8 nmol/liter was observed with a coefficient of variation less than 16% in the 20-320 nmol/liter. Specificity of the assay was very satisfying and a good correlation (r = 0.959) was noted for 33 human plasma samples between this assay and a commercial competitive radioimmunoassay.