Adaptation of the enzyme-multiplied immunoassay for methotrexate to the centrifugal analyzer.

We adapted the homogeneous enzyme-multiplied immunoassay for methotrexate to the centrifugal analyzer. The sensitivity of the assay has been extended from 200 nmol/L down to 12.5 nmol/L. Several protocols may be followed, depending on whether the samples to be tested are from patients on low- or high-dose methotrexate regimens. Precision, accuracy, and sensitivity were satisfactory. Comparison with the enzymic-inhibition method (x) gave the following least-squares regression: y = 1.002 x - 0.013 mumol/L; r2 = 0.9721; Sy/x = 0.014 mumol/L.