Valproic acid estimation by enzyme immunoassay

Blood samples from patients on long-term sodium valproate (Epilim) therapy were analysed for valproic acid by two procedures, enzyme immunoassay (EMIT) and gas-liquid chromatography (GLC). A critical evaluation of the effects of anticoagulants added to specimens was performed in addition to studies on reagent specificity, accuracy, and precision. EMIT valproic acid reagent showed high specificity, and there was a good correlation between results obtained by EMIT and GLC over a wide range of concentrations. The accuracy and precision of EMIT assay was good over the therapeutic range of valproic acid. The presence of the anticoagulant EDTA or of fluoride/oxalate produced a bias towards high results for valproic acid as compared with those obtained from the analysis of serum.