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

University of Birmingham, Birmingham, England, United Kingdom
BMJ (online) (Impact Factor: 17.45). 08/2007; 335(7612):190. DOI: 10.1136/bmj.39268.719780.BE
Source: PubMed


To assess the diagnostic accuracy and clinical utility of a simplified low cost method for measuring absolute and percentage CD4 counts with flow cytometry.
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.
Research laboratories and antiretroviral therapy clinic at a medical school and large government hospital in southern Malawi.
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.
Limits of agreement with 95% confidence intervals between index test and reference standards.
The limits of agreement for Blantyre count and TruCount were excellent (cell count -48.9 to 27.0 x10(9)/l for absolute counts in the CD4 range <400x10(9)/l and -2.42% to 2.37% for CD4 percentage). The assay was affordable with reagent costs per test of $0.44 ( pound0.22, euro0.33) 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 <200x10(9)/l. By contrast, 12 (20%) of 60 patients with stage III or IV disease had CD4 counts >350x10(9)/l.
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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    • "This is similar to the lymphocyte count above 500 cells/mL with limits of agreement approximately 6.2 ± 20.4%, as shown in Figure 3(b) (Bland-Altman), although this stratum showed a strong correlation (r = 0.81). Similarly, MacLennan et al. [20], assessing the use of flow cytometry to provide only the absolute count of CD4+ T cells (associated with total lymphocyte count in hematology analyzers to obtain the percentage of CD4+ T lymphocytes), obtained bias of 0.92% and limits of agreement between 5.83% and 7.66% through FacsCount and Multitest/Tubs Trucount method and in FACSCalibur flow cytometer, for the absolute count of CD4+ T cells below 200 cells/mL. "
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