Biotin at High Concentration Interferes with the LOCI Digoxin Assay but the PETINIA Phenytoin Assay Is Not Affected

Many automated immunoassays incorporate biotinylated antibodies and streptavidin-coated magnetic beads in the assay design. Biotin at elevated concentrations may interfere with these immunoassays. We evaluated potential interference of biotin on serum digoxin (LOCI assay utilizing biotinylated antibody) and phenytoin (PETINIA assay; no biotinylated antibody) measurements using the Vista 1500 analyzer. Aliquots of drug-free serum pool were supplemented with various biotin concentrations (range: 1 ng/mL to 250 ng/mL) followed by measuring apparent digoxin and phenytoin levels using appropriate immunoassays. In the second set of experiments, one serum pool was prepared from patients taking digoxin and another from patients taking phenytoin. Then aliquots of these serum pools were further supplemented with biotin followed by measuring digoxin or phenytoin concentrations. We observed apparent digoxin levels at 50 ng/mL biotin concentration or higher and also significant interference of biotin in serum digoxin measurement at a biotin concentration of 250 ng/mL. In contrast, we observed no interference of biotin in serum phenytoin measurement. We conclude that biotin interferes with the LOCI digoxin assay at a high concentration only.