Increased levels of HIV RNA detected in samples with viral loads close to the detection limit collected in Plasma Preparation Tubes (PPT).

Background: The accurate and reliable quantification of HIV RNA is an essential part of the management of HIV infected individuals, and elucidation of factors that may affect HIV RNA measurements, such as the use of Vacutainer Plasma Preparation Tubes (PPT), is crucial.

Objectives: The objective of this study was to determine if plasma samples with viral loads close to the lower limit of the dynamic range of the assay collected in PPT tubes had increased levels of HIV RNA as compared to samples collected in standard EDTA tubes.

Study Design: HIV RNA levels were compared in 112 paired plasma samples collected in PPT and standard EDTA tubes. All samples had been frozen prior to testing.

Results: Discrepancies between PPT and EDTA tubes did not occur for samples with high viral loads. However, in samples with viral loads close to the lower limit of the dynamic range, levels of HIV RNA detected were higher in a large proportion of PPT as compared to the corresponding EDTA plasma samples. Forty percent of plasma pairs had no detectable HIV RNA in the EDTA aliquot, but had low levels of HIV RNA in the corresponding PPT aliquot.

Conclusions: This prospective study underlines the need for cautious interpretation of small transient viral load changes in samples with values close to the detection limit.