Fluorescence polarization immunoassay for ethosuximide evaluated and compared with two other immunoassay techniques

We evaluated a new fluorescence polarization immunoassay (FPIA) for ethosuximide in the Abbott TDx and compared results with those by two other ethosuximide immunoassays, EMIT (Syva Co.) and aca (DuPont). The FPIA assay produced within- and between-day CVs of less than 5% at the low, medium, and high ranges of the standard curve. For the ethosuximide FPIA assay the standard curve was stable during the 47 days of the study. By all three methods, we analyzed 100 serum and plasma samples from patients who were receiving ethosuximide. The coefficient of determination (r2) for TDx versus EMIT was 0.973 (slope, 0.96; intercept, -0.80); for TDx vs aca it was 0.985 (slope, 1.00; intercept, -2.44); both relationships were statistically significant (p less than 0.05). Values for patient's specimens were significantly lower by the TDx than by the aca or EMIT methods (p less than 0.05).