WHO multicenter evaluation of FACSCount CD4 and Pima CD4 T-cell count systems: instrument performance and misclassification of HIV-infected patients.
BACKGROUND
CD4⁺ T-cell counts are used to screen and follow-up HIV-infected patients during treatment. As part of the World Health Organization prequalification program of diagnostics, we conducted an independent multicenter evaluation of the FACSCount CD4 and the Pima CD4, using the FACSCalibur as reference method.


METHODS
A total of 440 paired capillary and venous blood samples were collected from HIV-infected patients attending the HIV outpatient clinic in Antwerp, Belgium, and the HIV care and treatment center in Dar es Salam, Tanzania. Capillary blood was run on Pima analyzer, whereas venous blood was analyzed on FACSCount, Pima, and FACSCalibur instruments. Precision and agreement between methods were assessed.


RESULTS
The FACSCount CD4 results were in agreement with the FACSCalibur results with relative bias of 0.4% and 3.1% on absolute CD4 counts and an absolute bias of -0.6% and -1.1% on CD4% in Antwerp and Dar es Salam, respectively. The Pima CD4 results were in agreement with the FACSCalibur results with relative bias of -4.1% and -9.4% using venous blood and of -9.5% and -0.9% using capillary blood in Antwerp and Dar es Salam, respectively. At the threshold of 350 cells per microliter, the FACSCount CD4 and Pima CD4 using venous and capillary blood misclassified 7%, 9%, and 13% of patients, respectively.


CONCLUSIONS
The FACSCount CD4 provides reliable CD4 counts and CD4% and is suitable for monitoring adult and pediatric HIV patients in moderate-volume settings. The Pima CD4 is more suitable for screening eligible adult HIV patients for antiretroviral treatment initiation in low-volume laboratories.
*Laboratory of Immunology, Department of Biomedical Sciences, Institute of Tropical Medicine Antwerp, Antwerp, Belgium; †Unit of Immunology, Laboratory of Bacteriology Virology, Le Dantec University Teaching Hospital, University Cheikh Anta Diop, Dakar, Senegal; ‡Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium; §Department of Microbiology and Immunology, Muhimbili University of Health and Allied Sciences, Dar es Salam, Tanzania; and ‖World Health Organization, Geneva, Switzerland.
Djibril
D
Wade
Géraldine
G
Daneau
Said
S
Aboud
Gaby H
GH
Vercauteren
Willy S K
WS
Urassa
Luc
L
Kestens
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001530:Belgium / Q000453:epidemiology; D018791:CD4 Lymphocyte Count / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D015658:HIV Infections / Q000097:blood* / Q000175:diagnosis* / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013636:Tanzania / Q000453:epidemiology; D055815:Young Adult