Determination of methotrexate in serum by a rapid, fully mechanized enzyme immunoassay (EMIT).

A homogeneous enzyme immunoassay for the determination of methotrexate in serum (EMIT, Syva Corp.) was fully mechanized by the use of an Eppendorf analyzer 5010. Coefficients of variation from day to day were in the range 2--16%. A comparison of the results obtained by EMIT and a radioimmunoassay (Methotrexate 125 I Radioimmunoassay Kit, Diagnostic Biochemistry Inc.) in a series of 50 samples from patients showed a good correlation between both methods. The specificity of the EMIT assay appeared to be adequate. The time required for the determination of about 20 patient samples by this procedure was only about 80 minutes. From our clinical experimence the EMIT assay appears to be well suited for routine monitoring of methotrexate serum concentrations above 0.1 mumol/1 during intrathecal and high dose methotrexate therapy.