[Assay of free thyroxine by immunoenzyme method in general diseases]

In non thyroid illnesses the degree of serum FT4 levels perturbation may be variable according to the assay used. The performance of a new FT4 immunoenzymatic assay (Enzymmum test, BMF) was evaluated in 78 euthyroid controls and in 99 sick patients with renal insufficiency, severe diabetes, hypoalbuminemia, severe general disease or under heparinate treatment. Results were compared to two RIA assays: by immunoextraction (CA2), known to be little disturbed by hypoalbuminemia and considered as a reference method, and by a labelled antibody (MAB, Amerlex) easier to use. In controls mean values and T4 L confidence intervalls were comparable with the three assays. In patients FT4 levels were diminished in case of renal insufficiency but the mean values obtained by BMF and CA2 did not differ. FT4 levels of heparinate treated patients were elevated with BMF and CA2. Generally patients are better classified as euthyroid with the CA2 assay (5.6% misclassification) than with BMF (11.2%) or MAB (12.4%), particularly in case of serious disease. A good linear correlation was found between the three methods. With the new BMF assay results were grossly comparable to those obtained by other assays. However the determination of FT4 levels alone appeared no sufficient to characterize the patients thyroid status.