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.

Efficiency of the ortho VITROS assay for detection of hepatitis C virus-specific antibodies increased by elimination of supplemental testing of samples with very low sample-to-cutoff ratios.

The clinical significance of specimens with low sample-to-cutoff (S/Co) ratios in the Ortho VITROS chemiluminescence assay (CIA) for detection of antibodies to hepatitis C virus (HCV) was evaluated. In one study of 482 CIA-reactive samples, none of the 83 samples with S/Co ratios of < 5 was HCV RNA positive. In a subsequent study, 332 samples with S/Co ratios of between 1 and 20 were tested with the recombinant immunoblot assay (RIBA). None of the 163 samples with S/Co ratios of < 5 was RIBA positive, 83% were RIBA negative, and 28 samples (18%) were RIBA indeterminate. HCV RNA and/or clinical evidence of hepatitis was not found in the 27 indeterminate cases examined. These results show that over 99% of samples with very low S/Co ratios (< or = 5) have no evidence of HCV infection. Therefore, we suggest that the HCV antibody testing algorithm for the VITROS assay might be modified to eliminate supplemental testing of samples with very low S/Co ratios.

Inactivation of West Nile virus during serologic testing and transport.

Inactivation of West Nile virus (WNV) in enzyme-linked immunosorbent assay (ELISA) wash buffer at 37 degrees C was studied, as well as inactivation of WNV in cell culture medium over several days at an ambient temperature (28 degrees C). Aliquots of WNV were removed from the 37 degrees C ELISA wash buffer at 5, 15, 30, and 60 min for the former experiment, while daily aliquots of medium were sampled for the latter experiment. No virus was detected in the wash buffer at 30 and 60 min, while virus was readily detected from cell culture medium over this time. In addition, titers of WNV consistently dropped over a 7-day period at 28 degrees C compared to control suspensions of virus held at 4 degrees C. These observations indicate that WNV is readily inactivated in the presence of detergent-containing buffers. Furthermore, the viability loss at ambient temperature suggests that WNV is easily inactivated during routine transportation and testing of human body fluids such as serum and cerebrospinal fluid.