Evaluation of a new valproic acid enzyme immunoassay and comparison with a capillary gas-chromatographic method.

A new homogeneous immunoassay (EMIT) for valproic acid was evaluated. Besides testing the manual version of this enzyme immunoassay, we also developed two mechanized procedures for centrifugal analyzers (the CentrifiChem and the COBAS system), which take less time and are more precise than the manual method. Within-assay precision (CV) was 4.5% with the manual technique and 2% with the analyzers. Between-assay precision (CV) ranged from 4 to 13% for all three techniques. Accuracy of th manual method was checked by dilution and analytical recovery experiments. Our comparison of the EMIT results with those obtained by a comparison method (capillary gas chromatography) showed no significant difference. No interference from hemolysis, hyperbilirubinemia, or aliphatic amino acids was observed. At high concentrations of bile acids and with lipemic sera the analytical recovery rates decreased slightly, to 87% and 92%, respectively.