Using a fingerstick test for haematological monitoring in patients treated with clozapine.
Atkins M, McGuire P, Balgobin B, Patel P, Taylor D.
Therapeutic advances in psychopharmacology. 2021; 11(): 20451253211000865

Abstract

Background: Treatment with clozapine requires regular blood monitoring in order to minimise the risk of agranulocytosis. The demands on patients and clinicians associated with monitoring may be reduced by using point-of-care, as opposed to lab-based assessments. We assessed the utility of a device that can measure white blood cell (WBC) and neutrophil counts by capillary fingerstick blood. Method: The performance of a small, portable device (HemoCue(R) WBC DIFF System) was compared with that of a widely used laboratory analyser (ADVIA(R) 2120i) for measuring WBC and neutrophil counts. Patients with schizophrenia who were being treated with clozapine (n = 201) provided a fingerstick capillary sample and a venous sample for the respective assays. RESULTS: WBC counts and neutrophil counts from venous blood as determined by ADVIA 2120i, ranged from 3.0 x 10(9)/l to 19.5 x 10(9)/l, and 1.2 x 10(9)/l to 15.9 x 10(9)/l, respectively. There was a strong correlation between the results from venous and the capillary sample methods (WBC: R = 0.89, neutrophil: R = 0.92). By Passing-Bablok regression analysis, the slope of the association between ADVIA((R)) 2120i and HemoCue WBC DIFF for WBC was 1.0 [95% confidence interval (CI) 0.944-1.086], with intercept at -0.9 (95% CI -1.43 to -0.45). For neutrophils, the slope was 0.870 (95% CI 0.817-0.923), with intercept at -0.19 (95% CI -0.43 to 0.02). Overall, mean biases of -0.95 x 10(9)/l for WBC, and -0.91 x 10(9)/l for neutrophils were observed for the capillary blood method compared with the venous blood method. Below the clinical cutoff intervals for clozapine monitoring WBC (<3.5 x 10(9)/l) and neutrophils (<1.5 x 10(9)/l) these biases were -1.1 x 10(9)/l for WBC, and -0.25 x 10(9)/l for neutrophils. Conclusion: Results from the capillary blood HemoCue WBC DIFF analyser compared well with the venous blood ADVIA 2120i analyser for determining WBC and neutrophil counts. There was a slight overall bias, with the capillary method reporting lower values for both measures. Fingerstick point-of-care analysis is suitable for monitoring blood counts in patients on clozapine, although confirmatory standard venous testing is recommended for test results falling below accepted thresholds. CI - (c) The Author(s), 2021.



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