Capillary compared to venous blood sampling in clozapine treatment: patients׳ and healthcare practitioners׳ experiences with a point-of-care device.

Underuse of the antipsychotic clozapine for schizophrenia is an impediment to improving outcomes for patients. Because of its possible severe side effects, including granulocytopenia or even agranulocytosis, clozapine treatment entails regular WBC monitoring, which can be a major drawback for patients and practitioners. The HemoCue WBC DIFF system is a point-of-care device using capillary blood sampling which provides WBC counts with differentials, including granulocytes. We investigated if capillary sampling instead of conventional venous sampling might diminish the burden for patients and practitioners and motivate them to continue clozapine treatment. A randomized cross-over trial design was used to compare the two sampling methods. Patients׳ subjective experiences of various aspects of blood sampling were rated on a 10-cm visual analogue scale (VAS). Patients and practitioners were also asked if they had any preference for venous or capillary sampling and patients were asked if the sampling method influenced their motivation to continue clozapine treatment. Seventy-three patients were included in this study. Three dropped out before completion. The VAS ratings on all five aspects and the total burden experienced showed a consistent pattern favouring capillary blood sampling (p<0.001). This pattern was more pronounced for inpatients than for outpatients. Patients strongly preferred capillary testing (p<0.001). The method used moderately influenced their motivation for clozapine therapy. In this study patients tolerated capillary blood testing with a point-of-care device better than traditional venous sampling at a laboratory and practitioners also preferred it. Using this method might therefore boost clozapine prescription rates.