Point-of-care haematological monitoring during treatment with clozapine

Abstract

Abstract Objectives Patients treated with clozapine are required to have regular venous blood samples taken to measure white blood cell (WBC) and neutrophil counts to reduce the risk of agranulocytosis. The need for regular venous blood sampling can deter patients and clinicians from treatment with clozapine. Finger prick sampling offers patients a simpler and less invasive technique that is likely to be more acceptable. We undertook to evaluate a novel point of care testing (POCT) device which measures WBC and neutrophil counts using a small volume of capillary blood from a finger prick sample. Methods A total of 215 patients who were being treated with clozapine and were having a venous blood sample taken for haematological monitoring also provided a fingerprick capillary blood sample. The capillary and venous samples were tested using the Sight OLO® POCT analyser, and the venous sample also tested using a standard laboratory method. Results For both the WBC and the neutrophil counts, there was a strong correlation between the results from the standard laboratory venous method and the POCT assay (R=0.94 and 0.95, respectively for capillary blood samples, and R=0.98 for both WBC and neutrophil counts for venous blood samples). Compared with the standard laboratory venous blood method, mean biases were −1.0×109/L for WBC and −0.5×109/L for neutrophils for the capillary blood POCT method, and −0.4×109/L for WBC and −0.4×109/L for neutrophils for the venous blood POCT method. Overall, 6 of 215 (2.8%) of patients had levels below clozapine monitoring thresholds (WBC <3.5×109/L and Neutrophils <1.5×109/L) by capillary blood, and 5 (2.3%) by venous blood by POCT. Of these, 2 had sub-threshold counts on the standard laboratory method. Conclusions The POCT analyser provided results for both WBC and neutrophil counts that were comparable with those from a standard venous blood laboratory method. Using POCT devices may make haematological monitoring easier in patients being treated with clozapine, and thereby increase the use of clozapine in the treatment of schizophrenia.