Methods to increase the accuracy of the %CD4 T cell count in pediatric specimens from resource limited settings
R. Varro1, N. Bui1, M.T. Warns2, G. Campbell2, R.F. Pfeltz2, C. Bush2
1BD Biosciences, Reagent Development, San Jose, United States, 2BD Diagnostics, Sparks, United States
Background: Determination of CD4% is the main criteria for determining immunological function and in guiding treatment decisions in HIV infected children. A CD4 Stabilization Tube (ST) (Becton Dickinson (BD) Vacutainer Systems, Franklin Lakes, NJ) has been evaluated for maintaining CD4 count accuracy in specimens stored under different conditions of time and temperature and for the ability to kill infectious Mycobacteria species.
Methods: Three donor blood specimens were collected in the ST and in standard K3EDTA tubes. In triplicate, baseline specimens were stained and tested for CD4 and CD4%. Specimens stored at 4°C, 20°C, and 30°C were tested daily for 5 days In separate experiments, three strains of Mycobacterium (M. tuberculosis (H37Rv) and 99CDCE-30 and M. bovis TMC #407) at 200 - 2000 colony forming units were spiked into 5 mLs of blood and placed in ST. Survival was determined at 90 minutes, 7.5 hours, 48 hours and 5 days by transferring ST contents into BACTEC Myco/F Lytic blood culture bottles (BD) that were incubated 42 days in a BACTEC 9240 automated blood culture instrument.
Results: The mean total percent change in CD4 count in specimens stored in ST on day 5 compared to baseline was < 10% for all temperatures. No viable organisms from any of the three Mycobacteria tested were detected at any time point ranging from 90 minutes to 5 days in the CD4 tubes.
Conclusions: The BD FACSCount and CD4 reagent is a reliable system for testing HIV specimens stored in ST for up to 5 days at 30°C. Additionally, specimens stored in ST can be used for daily QC of CD4%. Blood samples stored in CD4 tubes for just 90 minutes killed Mycobacteria species. The ST may be useful as day-to-day QC controls and can reduce concerns about Mycobacterium in the blood specimens.
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