Comparison of LOCI Digoxin Assay and iDigoxin Assay for Rapid Detection of Convallatoxin, the Active Glycoside of the Lily of the Valley Plant

Abstract

ObjectiveLily of the Valley is a poisonous plant, used as an herbal remedy, with toxic effects due to convallatoxin, a cardiac glycoside. It has been reported that the LOCI digoxin assay, a luminescent oxygen channeling based digoxin immunoassay, has sufficient cross reactivity with Lily of the Valley extract, and the specific toxic component, convallatoxin. Yet, cross reactivity by the iDigoxin immunoassay, a chemiluminescent microparticle immunoassay, has not been reported in the literature. In this study, we evaluate iDigoxin immunoassay's ability to detect Lily of the Valley and convallatoxin, and compare these findings to those measured by the LOCI digoxin assay.Materials and MethodsAliquots of drug free and digoxin serum pools were supplemented with microliter amounts of Lily of the Valley extract or nanogram quantities of convallatoxin. Digoxin concentrations were measured using the iDigoxin immunoassay applied to the ARCHITECT i2000SR analyzer (Cabbott Laboratories), and the LOCI digoxin assay applied to the Vista 1500 analyzer (Siemens Diagnostics).ResultsThe iDigoxin assay measured significantly higher apparent digoxin concentrations than the LOCI digoxin assay in all supplemented aliquots. Also, the LOCI digoxin assay demonstrated bi‐directional interference with aliquots of a digoxin pool supplemented with various amounts of convallatoxin. However, with the iDigoxin assay all values were falsely elevated, indicating positive interference only.ConclusionsThe iDigoxin assay can be used for rapid detection of convallatoxin and Lily of the Valley in human serum. Also, the iDigoxin assay is more sensitive than the LOCI digoxin assay in convallatoxin detection.