Haematological point of care testing for clozapine monitoring

Abstract

BackgroundClozapine treatment requires regular full blood counts (FBC) because of the risk of agranulocytosis. Traditionally, FBCs use venous blood samples but the need for frequent venepuncture adversely affects adherence. We investigated the utility of a point of care testing (POCT) finger prick method for clozapine patients. MethodPatients being treated with clozapine, who were having a venous blood sample taken for haematological monitoring, also provided a fingerprick capillary blood sample. The PixCell HemoScreen® POCT analyser was used to test both the capillary and venous samples, and the venous sample was also tested using a standard laboratory method. ResultsWe completed FBCs on 226 patients. We found strong correlations between the results from the standard laboratory venous method and the POCT capillary and venous assays for WBC (R = 0.96 & R = 0.99), neutrophils (R = 0.96 & R = 0.97) and eosinophils (R = 0.94 & R = 0.94). Compared with the standard laboratory venous blood method, mean biases for capillary blood POCT method were −0.56 × 109/L for WBC, −0.39 × 109/L for neutrophils, and −0.01 × 109/L for eosinophils. Mean biases for venous blood POCT method were −0.004 × 109/L for WBC, −0.28 × 109/L for neutrophils, and 0.01 × 109/L for eosinophils. Of the 226 patients tested, 10 (4.4%) had levels below clozapine monitoring thresholds (WBC <3.5 × 109/L and Neutrophils <1.5 × 109/L) by capillary blood, and 4 (1.8%) by venous blood by POCT. The standard laboratory method showed 3 of these to be sub-threshold. All cases of neutropenia were identified by capillary and venous POCT. ConclusionThe PixCell HemoScreen® POCT analyser provided results that were comparable with those from a standard venous blood laboratory method for WBC, neutrophil and eosinophil counts. The availability of an accurate capillary monitoring method may result in increased clozapine uptake and better clozapine adherence.