DETERMINATION OF THYROXINE (T4) IN SERUM WITH A HETEROLOGOUS ENZYME IMMUNOASSAY - RESULTS OF AN EVALUATION BY 7 LABORATORIES

  • 1 January 1979
    • journal article
    • research article
    • Vol. 17  (7) , 471-481
Abstract
An evaluation of a heterologous enzyme immunoassay for the determination of total thyroxine in serum by a group of 7 clinical chemical laboratories is described. The test follows the principles of the enzyme linked immunosorbent assay (ELISA) and uses peroxidases as a marker. The evaluation of analytical reliability yielded several results within the analytical range from 39-322 nmol/l. Within-batch precision ranged from 3.1-10.4% (coefficient of variation) with single analyses. Between-batch precision ranged from 3.7-20.4% with single analyses. Between-laboratories precision ranged from 5.4-6.8%. Pure thyroxine, added to serum or thyroxine-free serum, gave recoveries between 93-120%. Analysis of control sera gave results essentially comparable to the assigned values based upon radioimmunoassays. Analysis of 288 clinical sera gave slightly higher results by the enzyme immunoassay than by the analogous radioimmunoassay from the same manufacturer. Comparison with other methods of analysis (radioimmunoassays, competitive protein ligand assays, hormonal iodine assay) yielded partly comparable, partly higher results. Comparison with the enzyme multiplied immunoassay technique (EMIT) led to comparable results. Interference due to hyperlipemia or hemolysis was not observed. There may be an interference in hyperbilirubinaemic sera, due to an unknown factor. With respect to practicability, the ELISA-test compares favorably with the analogous solid phase radioimmunoassay. The main differences are the absence of radioactive material and a longer shelf-life of reagents. Following the manual procedure, the time taken to perform the enzyme immunoassay is slightly longer than for the analogous radioimmunoassay.