BMJ  2007;335:190 (28 July), doi:10.1136/bmj.39268.719780.BE (published 17 July 2007)

Research

Diagnostic accuracy and clinical utility of a simplified low cost method of counting CD4 cells with flow cytometry in Malawi: diagnostic accuracy study

¹ Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, PO Box 30096, Blantyre 3, Malawi, and Medical Research Council Centre for Immune Regulation, Division of Immunity and Infection, University of Birmingham, Birmingham B15 2TT, ² Medical Research Council Centre for Immune Regulation, Division of Immunity and Infection, University of Birmingham, Birmingham B15 2TT, ³ Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, PO Box 30096, Blantyre 3, Malawi, ⁴ Department of Medicine, College of Medicine, University of Malawi, Private Bag 360, Blantyre 3, Malawi

Objectives To assess the diagnostic accuracy and clinical utility of a simplified low cost method for measuring absolute and percentage CD4 counts with flow cytometry.

Design A CD4 counting method (Blantyre count) using a CD4 and CD45 antibody combination with reduced blood and reagent volumes. Diagnostic accuracy was assessed by measuring agreement of the index test with two other assays (TruCount and FACSCount). Clinical utility was investigated by comparing CD4 counts with the new assay with WHO clinical staging in patients with HIV.

Setting Research laboratories and antiretroviral therapy clinic at a medical school and large government hospital in southern Malawi.

Participants Assay comparisons were performed on consecutive blood samples sent for CD4 counting from 129 patients with HIV. Comparison of CD4 count with staging was conducted on 253 consecutive new patients attending the antiretroviral therapy clinic.

Main outcome measures Limits of agreement with 95% confidence intervals between index test and reference standards.

Results The limits of agreement for Blantyre count and TruCount were excellent (cell count –48.9 to 27.0 cells/µl for absolute counts in the CD4 range <400 cells/µl and –2.42% to 2.37% for CD4 percentage). The assay was affordable with reagent costs per test of $0.44 (£0.22, 0.33) for both absolute count and CD4 percentage, and $0.11 for CD4 percentage alone. Of 193 patients with clinical stage I or II disease, who were ineligible for antiretroviral therapy by clinical staging criteria, 73 (38%) had CD4 counts <200 cells/µl. By contrast, 12 (20%) of 60 patients with stage III or IV disease had CD4 counts >350 cells/µl.

Conclusions This simplified method of counting CD4 cells with flow cytometry has good agreement with established commercial assays, is affordable for routine clinical use in Africa, and could improve clinical decision making in patients with HIV.

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Rapid Responses:

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CD4 counts and HIV therapy: flow cytometry is not the answer

Michel Erlewyn-Lajeunesse
bmj.com, 30 Jul 2007 [Full text]

Consolidation of affordable flow cytometric PanLeucogating testing protocols to ensure sustainable reliable CD4 monitoring in Southern Africa.

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Use of fixed, propidium-iodide -stained cells, produced in house, to further reduce the cost of the Blantyre count for CD4+ cells

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bmj.com, 8 Sep 2007 [Full text]

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