[Clinical significance of changing from a second to a third generation thyroid stimulating hormone (TSH) assay].

In recent years new sensitive immunochemoluminiscentic methods to measure thyroid stimulating hormone, TSH have been introduced. In this investigation we have made a comparison between an older, less sensitive, second generation TSH assay and a new, sensitive, third generation TSH assay in order to evaluate if new information of clinical value is obtained. We found that 20% of all the sera that were sent to the laboratory for TSH measurement showed low values. In the sera with low TSH concentration a great variation was observed between the "correct" values found with the third generation assay and the values found with the less sensitive second generation assay. We conclude, that since many sera sent to a routine laboratory have low TSH concentrations, and since it is of clinical importance to know the correct TSH value in many different patient categories, a third generation TSH assay is recommended in the daily routine.