Comparison of pituitary and recombinant human thyroid-stimulating hormone (rhTSH) in a multicenter collaborative study: establishment of the first World Health Organization reference reagent for rhTSH.

BACKGROUND The increasing use of recombinant-DNA-derived materials in therapy and diagnosis poses a new challenge for biological standardization, that of developing reference preparations appropriate for both the native and recombinant products. Here we report the results of an international collaborative study that was carried out under the auspices of WHO to assess the suitability of a preparation of recombinant thyroid-stimulating hormone (rTSH; 94/674) to serve as a potential standard for the calibration of diagnostic immunoassays compared with the International Reference Preparation (IRP) for human TSH (80/558). METHODS Coded samples were provided to the 33 laboratories in the study, and participants were asked to perform TSH assays currently in use in their laboratories. Twenty-eight laboratories contributed 93 immunoassays in 41 different method-laboratory combinations, and an additional 5 laboratories contributed bioassay data. All data were analyzed centrally at the National Institute for Biological Standards and Control. RESULTS The results obtained in different laboratories and with different assay systems revealed significant variability between estimates of rTSH relative to the IRP. These ranged from 5. 51 mIU (95% limits, 3.95-7.67 mIU) per ampoule by RIA to 7.15 mIU (95% limits, 6.7-7.63 mIU) per ampoule by immunofluorometric assay. However, the results showed that the assignment of a value of 6.70 mIU per ampoule of 94/674 would give reasonable continuity with the IRP in many assay systems. CONCLUSIONS The preparation was established as the First WHO Reference Reagent for TSH, human, recombinant, to provide a means of validating assay performance and to maintain continuity with the IRP without compromising clinical data.