Report on a common survey in clinical laboratories in Belgium and in The Netherlands: immunoassays.

A common survey for immunoassays was organized for Belgian and Dutch laboratories. We compared the different statistical approaches used in the two schemes; both approaches lead to comparable results. Differences in overall consensus values and overall precision are related to a different selection of kits in the two countries.

The immunofluorometric TSH assay as first-line test for suspected thyroid dysfunction.

In this study of 103 patients with suspected thyroid dysfunction, the diagnostic value of a single basal immunofluorometric (IFMA) TSH measurement was evaluated and compared with the classical TRH test with RIA-TSH measurements, plasma TT4 concentrations and FT4I. A single basal TSH determination accurately predicted the TRH-stimulated TSH response, making the TRH test redundant in most patients. Because undetectable basal TSH did not always exclude a small rise in TSH, the TRH test could still be indicated in patients receiving thyroxine suppression therapy for thyroid cancer.

Analytical evaluation of four sensitive assays of thyrotropin, including effects of variations in patient sampling.

Four immunometric kits for thyrotropin with detection limits below 0.1 milli-int. unit/L were evaluated with respect to accuracy, precision, specificity, matrix effects, and high-dose "hook" effect.

The need for a sufficient number of low level sera in comparisons of different serum vitamin B12 assays.

Eight radiochemical methods for the assay of vitamin B12 in serum were compared with the microbiological assay with Lactobacillus leichmannii ATCC 7830 using 198 individual sera of patients. There was a good agreement between the results of most samples with some kits and the microbiological assay. However, especially in the sera of vitamin B12-deficient patients large discrepancies between the results could occur.

A comparative study of free thyroxine estimations.

Two commercial methods (Immophase, Corning and FT4, Lepetit) for the measurement of free thyroxine (FT4) in serum have been experimentally evaluated. Ease of handling and rapidity were satisfactory. Precision profiles showed intra-assay coefficients of variation not exceeding 5% over the entire measurement range (0-70 pmol/l) for both methods.