Abstract
BACKGROUND: CD4 T-cell counts are still widely used to assess treatment eligibility and follow-up of HIV-infected patients. The World Health Organization (WHO) prequalification of in vitro diagnostics requested a manufacturer independent laboratory evaluation of the analytical performance at the Institute of Tropical Medicine (ITM) Antwerp, Belgium, of the Muse Auto CD4/CD4% system (Millipore), a new small capillary-flow cytometer dedicated to count absolute CD4-T cells and percentages in venous blood samples from HIV-infected patients. METHODS: Two hundred and fifty (250) patients were recruited from the HIV outpatient clinic at ITM. Accuracy and precision of CD4 T cell counting on fresh EDTA anticoagulated venous blood samples were assessed in the laboratory on a Muse Auto CD4/CD4% system. Extensive precision analyses were performed both on fresh blood and on normal and low stabilized whole blood controls. Accuracy ((bias) was assessed by comparing results from Muse CD4/CD4% to the reference (single-platform FACSCalibur). Clinical misclassification was measured at 500, 350, 200 and 100 cells/μL thresholds. RESULTS: Intra-assay precision was < 5%, and inter-assay was < 9%. CD4 T cell counts measured on Muse Auto CD4/CD4% System and on the reference instrument resulted in regression slopes of 0.97 for absolute counts and 1.03 for CD4 T cell percentages and a correlation coefficient of 0.99 for both. The average absolute bias as compared to the reference was negligible (4 cells/μL or 0.5%). The absolute average bias on CD4 T cell percentages was < 1%. Clinical misclassification at different CD4 T cell thresholds was small resulting in sensitivities and specificities equal or >90% at all thresholds except at 100 cells/μL (sensitivity = 87%). All samples could be analyzed as there was no repetitive rejection errors recorded. CONCLUSIONS: The Muse Auto CD4/CD4% System performed very well on fresh venous blood samples and met all WHO acceptance criteria for analytical performance of CD4 technologies.