EFFECT OF SPECIMEN STORAGE ON ABSOLUTE CD4 COUNTS

We have evaluated the effect of specimen storage on absolute CD4 count s by a commercially available manual assay. This assay utilizes latex particles coated with CD4 monoclonal antibodies that are mixed with ly mphocytes in whole blood. Thirty blood samples were analyzed on days 1 , 2, 4, and 7 postcollection. Linear regression analysis and Pearson c orrelation coefficients were used to determine the relationship betwee n the absolute CD4 count and the storage time after sample collection. There was a significant decrease in absolute CD4 counts from baseline over time, dropping 3.6% at day 2, 10.1% at day 4, and 18.8% at day 7 . However, the standard error of the B coefficient was constant [SE (B ) = 0.031] up to day 4, indicating that reliable estimates of the base line CD4 counts could be made from the CD4 counts determined up to day 4 from the time of sample collection. In addition to being simple, ra pid, and inexpensive, the manual assay is capable of giving a reliable absolute CD4 count after specimen storage of up to 4 days. The applic ation of this assay in the limited facilities of developing countries' laboratories is attractive.