Evaluation of Cyto-Chex® reagent on the stability of T CD4+ and T CD8+ cell markers in whole blood samples
Background: In Brazil and other moderately resourced settings flow cytometry can be made available in central laboratories to monitor immune status in HIV-infected patients. However, specimens must typically be analyzed within 24 hours after phlebotomy, which dramatically limits availability of this testing. We evaluated the Cyto-Chex® reagent, a stabilizer that preserves the white blood cells markers.
Methods: The samples were obtained from three clinical centers located in south Brazil, during June-July/2008, with separate aliquots stored in EDTA and Cyto-Chex BCT at room temperature (12°C-27°C) until the moment of analysis. CD4+ and CD8+ T cell counts were performed on EDTA specimens within 24 hours; Cyto-Chex® BCT (CCBCT) samples were analyzed over different time periods (3 to 5, 7, 9-11 days post collection). Assays were performed using BD Facs Count equipment.
Results: Of forty-eight samples collected into CCBCT, forty-six (95.8%) gave valid CD4/CD8 results. Both CD4 and CD8 on fresh specimens were highly correlated whether in CCBCT or EDTA (CD4 r2=.965; CD8 r2=.958, p< .001); Fresh blood CD4 counts were similar but fresh blood CD8 counts were significantly lower on CCBCT specimens than on EDTA (mean difference: -34.81 CD8 cells/mm3; p< .001). We detected no change in CD4 or CD8 counts over time.
Conclusions: The Cyto-Chex® reagent appears to maintain integrity of white blood cell antigens for CD4 and CD8 enumeration for up to 11 days, providing additional time for sample shipment and processing to a flow cytometry laboratory. This could be an important tool in resource-poor settings where refrigeration and other ancillary laboratory equipment may not be available at collection sites.
B.S. Velho1, D. Pellenz1, L.G.A. Borges1, A.C. Vanni1, S.K. Kato1, L.R. Motta1, R.D. Sperhacke1, C.D. Pilcher2, R.S. Souza1
1Universidade de Caxias do Sul, Laboratório de Pesquisa em HIV/AIDS, Caxias do Sul, RS, Brazil, 2University of California-San Francisco, San Francisco, United States