Diagnostic accuracy and clinical utility of a simplified low cost method of counting CD4 cells with flow cytometry in Malawi: diagnostic accuracy study.
OBJECTIVE
To assess the diagnostic accuracy and clinical utility of a simplified low cost method for measuring absolute and percentage CD4 counts with flow cytometry.


METHODS
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.


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


METHODS
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.


METHODS
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 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.


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.
MacLennan
Calman A
CA
Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, PO Box 30096, Blantyre 3, Malawi. c.maclennan@bham.ac.uk
Liu
Michael K P
MK
White
Sarah A
SA
van Oosterhout
Joep J G
JJ
Simukonda
Felanji
F
Bwanali
Joseph
J
Moore
Michael J
MJ
Zijlstra
Eduard E
EE
Drayson
Mark T
MT
Molyneux
Malcolm E
ME
D000328:Adult; D015496:CD4-Positive T-Lymphocytes; D003362:Cost-Benefit Analysis; D005434:Flow Cytometry / Q000191:economics / Q000592:standards; D015658:HIV Infections / Q000175:diagnosis*; D006801:Humans; D018655:Lymphocyte Count / Q000191:economics / Q000592:standards*; D008295:Malawi; D011786:Quality Control; D012015:Reference Standards