Results by fluorescent immunoassay for phenytoin compared with those by enzyme immunoassay, liquid chromatography, and discrete analysis (Dupont aca).

We describe the Ames Fluorescent Enzyme Immunoassay procedure for the detection of phenytoin in serum, and compare the results with it with those by enzyme immunoassay(EMIT), "high-pressure" liquid chromatography, and the Dupont aca. Sera from 48 patients who were receiving phenytoin were promptly analyzed in duplicate by EMIT, frozen, then assayed within four weeks by the other three methods. Correlation was good between results by the fluorescent immunoassay and the other methods. The fluorescent immunoassay procedure is sensitive and requires a small sample volume (100 microliters). Sample reading time can be shortened from 30 to 15 s as the technician becomes more proficient, with no sacrifice of accuracy. The procedure is fast, easy to perform, specific, sensitive, and inexpensive; involves no radioactivity; and requires no temperature control. It is the current method of choice for detection of phenytoin in serum, in terms of precision and accuracy.