STABILITIES OF QUANTITATIVE PLASMA CULTURE FOR HUMAN-IMMUNODEFICIENCY-VIRUS, RNA, AND P24 ANTIGEN FROM SAMPLES COLLECTED IN VACUTAINER CPT AND STANDARD VACUTAINER TUBES

We evaluated the stability of human immunodeficiency virus (HIV) load markers from blood samples collected in VACUTAINER CPT or standard VAC UTAINER brand tubes using sodium heparin or sodium citrate as anticoag ulants. Quantitative plasma culture and p24 antigen concentrations wer e determined, and HIV RNA levels in plasma were measured by both rever se transcription-PCR-enzyme-linked immunosorbent assay (RT-PCR-ELISA) and branched DNA methods. All tubes were stored at room temperature fo r analysis at 2, 24, 48, and 72 h after the blood samples were drawn. No difference was seen between tube types with respect to the HIV tite r in plasma or the positivity rate for all samples that demonstrated a fall in titer over time. Unbound p24 antigen levels in plasma decreas ed during the initial 48-h period in both tube types. Immune complex-d issociated p24 antigen levels decreased in CPT tubes but not in standa rd VACUTAINER tubes. The HIV RNA copy number in plasma measured by RT- PCR-ELISA was stable in most subjects and was significantly higher in CPT tubes than in standard VACUTAINER tubes at 24 and 72 h after the b lood samples were drawn. The branched DNA probe assay detected a signi ficant decline in HIV RNA equivalents in plasma over 72 h in both coll ection tubes, the decline being more dramatic in the standard VACUTAIN ER tube than the CPT tube. Overall, interday variability suggests that samples collected for a particular assay should be processed at the s ame time after blood is drawn and that a particular tube type be used throughout a given study.