*2.1. Plasma*

Plasma is the supernatant after the cellular components of the anti-coagulated blood are removed after centrifugation. Plasma specimens are usually collected for molecular assays such as HIVDR testing, which examines the HIV viral RNA it contains. Plasma has the highest viral RNA concentration among all analytes applied in HIVDRT. The viral population in plasma best represents the cell-free, replication-competent, circulating HIV viruses in the patients. HIV viral RNA in plasma remains stable in ambient temperature and long-term storage under freezing conditions [5–7].

Plasma is the gold standard analyte most commonly used for HIVDRT [8]. It serves all clinical, surveillance, and research HIVDRT needs. All breakthroughs in HIVDRT assay development and validation were first established using plasma and then applied to other analytes. The prevention of blood clotting maximizes the number of viral templates available in plasma for HIV genotyping. This is particularly important for specimens collected from ART-treated individuals whose VLs could be extremely low. It is noteworthy that ethylenediaminetetraacetic acid (EDTA), but not heparin, should be used as the anticoagulant if a molecular assay such as HIVDRT is to be performed on the derived plasma. This is due to the inhibitory effect of heparin in the downstream polymerase chain reaction (PCR) amplifications [9,10].
