Hydroxyzine and cetirizine interfere with the PENTINA carbamazepine assay but not with the ADVIA CENTEUR carbamazepine assay.

Because of a published report indicating significant interference of hydroxyzine with the particle-enhanced turbidimetric inhibition immunoassay (PENTINA) carbamazepine assay, we investigated whether such interference can be avoided by using the ADVIA Centaur carbamazepine assay. Both the Dimension Vista analyzer and ADVIA Centaur analyzer are available from Siemens Diagnostics. Aliquots of a drug-free serum pool were supplemented with various concentrations of hydroxyzine or cetirizine (0.05 microg/mL to 20 microg/mL covering therapeutic and toxic levels in serum) followed by analysis using both assays. We observed significant apparent carbamazepine concentrations using the PENTINA assay but no apparent carbamazepine level using the ADVIA Centaur assay. Because crossreactivity should be studied in the presence of the primary analyte, we also prepared a serum carbamazepine pool from patients receiving carbamazepine and then supplemented aliquots of this pool with various amounts of hydroxyzine or cetirizine followed by reanalyzing carbamazepine concentration using both assays. We observed falsely elevated carbamazepine values using the PENTINA assay but no interference was observed using the ADVIA Centaur assay. However, the falsely elevated carbamazepine values using the PENTINA assay were clinically significant at hydroxyzine or cetirizine concentrations expected in patients with severe overdoses with these drugs. We conclude that the ADVIA Centaur carbamazepine assay is free from interference of both hydroxyzine and cetirizine.