Objective: To evaluate a manual method (Cytosphere) for quantifying CD4+ T-cell numbers.
Design: Cross-sectional study of HIV-1-seronegative and HIV-1-seropositive individuals evaluated for absolute CD4 counts by both standardized flow cytometric measurements and manual Cytosphere technology using a hemacytometer.
Setting: University research hospitals in both the United States and Africa.
Patients, participants: Blood specimens from 382 patients were evaluated. These were broken down into 294 samples obtained from HIV-1-seropositive patients and 88 samples obtained from HIV-1-seronegative patients.
Outcome measured: Absolute CD4 cell number.
Results: Evaluation of samples obtained from HIV-1 patients in both the United States and Africa demonstrated an overall correlation of the Cytosphere assay with flow cytometry of 0.912 (95% confidence interval, 0.895-0.928; P < 0.001). When samples were stratified based on CD4+ T-cell counts determined by flow cytometry, the Cytosphere assay had a 96% predictive value for correctly identifying individuals with CD4 T-cell counts > 200 x 10(6)/l and a 92% predictive value for correctly identifying individuals with CD4 T-cell counts < 200 x 10(6)/l.
Conclusions: This assay appears to have the potential for the quantitation of CD4 cells in the limited laboratory facilities in developing countries and to have a strong correlation with standard flow cytometric technology.
PIP: Clinicians took blood samples from 294 HIV-1 seropositive patients and 88 HIV-1 seronegative patients at Cornell University Medical College and The New York Hospital in New York City, Rush-Presbyterian-St. Luke's Medical Center in Chicago, and Makerere University Medical school in Kampala, Uganda, to assess a manual method's (Cytosphere) ability to accurately determine the CD4+ T-cell count. The Cytosphere assay uses latex beads coated with CD4 antibody which are combined with anticoagulated whole blood followed by red cell lysis. A hemacytometer then counts the bead-coated cells. The average technologist only needs 1-3 days of training (20 CD4 practice assays/days) in the Cytosphere assay. The minimal equipment required for the assay are a pipette, a hemacytometer, and a light microscope. The lysing agent inactivates HIV-1. The overall correlation between the standard flow cytometry method and the Cytosphere assay stood at 0.912 and was significant (p .001). When the researchers stratified the samples based on CD4+ T-cell counts defined by flow cytometry, the predictive values of the Cytosphere assay for correctly identifying patients with CD4 T-cell counts greater or less than 200 x 1 million/1 were 96% and 92%, respectively. These findings suggested that the Cytosphere assay has the potential to quantify CD4 cells in the limited laboratories in developing countries. Larger longitudinal studies of HIV seropositive people in developing countries are needed to test the reliability and reproducibility of the assay.