Near-patient rapid assay of carbamazepine concentration

Abstract

Rapid turnaround testing of carbamazepine (CBZ) concentration helps the clinician assess patients efficiently. The Biotrack (BT) therapeutic drug monitor uses an automated turbidimetric latex agglutination assay of hemolyzed whole blood and reports the corresponding serum drug concentration within 3 min of sample application. We compared BT results for 53 patients with serum CBZ measurements made with the Abbott TDx fluorescence polarization immunoassay (FPIA) system. Mean BT concentration was 9.5 μg/ml (range, 2.8–18.3 μg/ml); one sample was reported “below 2.0 μg/ml” (FPIA = 1.1 μg/ml). Mean FPIA concentration of the 52 BT-quantifiable samples was 8.7 μg/ml (range, 2.8–18.0 μg/ml). Correlation of BT with FPIA was high ( r = 0.96). BT results had a bias of 0.8 μg/ml [95% confidence intervals (CI) = 0.6 to 0.9 μg/ml]; median absolute error relative to FPIA was 0.6 μg/ml. Variations within the normal range for hematocrit, albumin, and creatinine had minimal effect on accuracy. As compared with a high-pressure liquid chromatographic (HPLC) assay, the BT assay showed less cross-reactivity than did FPIA to increased concentrations of the CBZ metabolite, carbamazepine-10,11-epoxide (CBZE). Assays performed on samples from 15 other patients not receiving CBZ were all <2.0 μg/ml. The BT assay is sufficiently accurate for clinical monitoring of CBZ concentrations