Evaluation of Portable Point-of-Care CD4 Counter with High Sensitivity for Detecting Patients Eligible for Antiretroviral Therapy

Background: Accurate, inexpensive point-of-care CD4+ T cell testing technologies are needed that can deliver CD4+ T cell results at lower level health centers or community outreach voluntary counseling and testing. We sought to evaluate a point-of-care CD4+ T cell counter, the Pima CD4 Test System, a portable, battery-operated bench-top instrument that is designed to use finger stick blood samples suitable for field use in conjunction with rapid HIV testing. Methods: Duplicate measurements were performed on both capillary and venous samples using Pima CD4 analyzers, compared to the BD FACSCalibur (reference method). The mean bias was estimated by paired Student's t-test. Bland Altman plots were used to assess agreement. Results: 206 participants were enrolled with a median CD4 count of 396 (range; 18-1500). The finger stick PIMA had a mean bias of -66.3 cells/mu L (95% CI -83-4-49.2, P<0.001) compared to the FACSCalibur; the bias was smaller at lower CD4 counts (0-250 cells/mL) with a mean bias of -10.8 (95% CI -27.3-+5.6, P = 0.198), and much greater at higher CD4 cell counts (>500 cells/mu L) with a mean bias of -120.6 (95% CI -162.8, -78.4, P<0.001). The sensitivity (95% CI) of the Pima CD4 analyzer was 96.3% (79.1-99.8%) for a <250 cells/ul cut-off with a negative predictive value of 99.2% (95.1-99.9%). Conclusions: The Pima CD4 finger stick test is an easy-to-use, portable, relatively fast device to test CD4+ T cell counts in the field. Issues of negatively-biased CD4 cell counts especially at higher absolute numbers will limit its utility for longitudinal immunologic response to ART. The high sensitivity and negative predictive value of the test makes it an attractive option for field use to identify patients eligible for ART, thus potentially reducing delays in linkage to care and ART initiation.