CD4 estimating reagents in dry format are compatible with conventional flow cytometer; FACSCalibur for estimation of absolute CD4 count & percentages

Background & objectives: Reliable CD4 counts are important for successful implementation of antiretroviral treatment (ART). Availability of dry CD4 reagents can eliminate cold chain requirement reducing shipment and storage cost. An attempt was made in this study to validate the ReaPan and Rea T Count dry reagents developed by ReaMetrix against the original BD Biosciences liquid reagents. Method: Absolute counts and percentages of CD4, CD8 and CD3 + T cells obtained in 100 HIV infected individuals using the test and reference reagents were analyzed for correlation and agreement using Pearson's correlation and Bland Altman bias analysis. The stability of the reagents and of the stained samples was analyzed at ambient temperature and at 37 degrees C. Results: The absolute CD4 + T cell count and percentages obtained using test and reference reagents showed correlation coefficients ranging from 833 to 981. A mean bias between dry and reference reagents ranged from 0.8 to 26.4. The ReaPan and Rea T Count reagents were stable up to one month at 37 degrees C also. The samples stained with ReaPan reagents were stable at ambient temperature till day 7 whereas the samples stained with Rea T Count reagents were stable at ambient temperature and at 37 degrees C for 10 days. Interpretation & conclusions: The ReaPan dry reagents can be used on existing FACSCalibur machines with additional training on Cell Quest Pro software without incurring any additional equipment cost and this can eliminate the requirement of cold chain during transport and on site storage. The stability of the stained samples has great clinical significance preventing redrawing of the blood samples from the patients.