Evaluation of enhanced luminescence immunoenzymometric assays (lia) for ferritin and free T4

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Abstract
The Amerlite enhanced luminescence immunoenzymometric assays (LIA) for ferritin and free T4 (FT4) have been evaluated. The LIA assay system employs a two‐site binding approach in which one antibody is coated on the interior of plastic microtiter wells and another antibody, or antigen, is tagged with horseradish peroxidase (HRPO). Signal, proportional to the amount of patient analyte, is produced when the HRPO catalyzes the oxidation of luminol resulting in light production. The light signal is increased in magnitude by the incorporation of an enhancing agent which also greatly prolongs the lifetime of the signal. Light production is monitored by an automated luminometer which uses a stored calibration curve to calculate patient results. FT4 within‐run coefficients of variation (CVs) ranged from 2.7% to‐ 6.6%; day‐to day CVs from 6% to 15.5% for three levels of control. Sensitivity is 0.03 ng/dl. T3 concentrations up to 8 ng/ml produced no cross‐reactivity. Dilutional linearity was exhibited. Lipemia and icterus produced positive interferences. Linear regression analysis of Amerlite and radioimmunoassay (RIA) FT4 values yielded the following values: Amerlite = 0.63 RIA ‐ 0.2, r = .87, n = 79. Ferritin within‐run CVs ranged from 4.9% to 10.5%; day‐to‐day CVs from 5.8‐12.5% for three levels of control. Sensitivity is less than 1 ng/ml. Recoveries ranged from 93% to 106% (av. = 99.4%). Dilutional linearity was exhibited. Lipemia caused a positive interference; hemoglobin caused a negative interference. Linear regression analysis of Amerlite and RIA ferritin values yielded the following values: Amerlite = 1.0 RIA + 11.1, r = .96, n = 55.