[Determining the methotrexate concentration in serum with the fluorescence polarization immunoassay (FPIA)--a...

The determination of methotrexate in serum was performed by the fluorescence polarization immunoassay (FPIA) and the enzyme immunoassay (EMIT). Both methods showed a good precision and accuracy. The investigation was carried out in 138 sera with a methotrexate concentration up to 1,400 mumol/l. The comparison of the two methods in 100 sera with a methotrexate concentration up to 5 mumol/l showed a good correlation (correlation coefficient r = 0.9798). Close correlation (correlation coefficient r = 0.9845) was also found in 38 sera with a methotrexate concentration between 5 and 1,400 mumol/l. Discussion of the FPIA and EMIT methods.