The Impact of Universal Transport Media and Viral Transport Media Liquid Samples on a SARS-CoV-2 Rapid Antigen Test

Author(s): Jeff A. Mayfield, Jose Ortiz, David J. Ledden*

Background: SARS-CoV-2 rapid antigen test evaluations require the use of samples that have been collected and stored in a variety of media and tested using non-ideal methods. The issues with this are sample dilution (e.g., decreased analyte concentration), dilution of extraction buffer components (surfactant, pH, and ionic strength) and UTM/VTM formula components that may interfere with test results, often producing false positive outcomes.

Methods: To evaluate the impact from these issues, a variety of materials were tested on the CLINITEST® Rapid COVID-19 Antigen Test (Manufactured by Healgen Scientific LLC, distributed by Siemens Healthcare Diagnostics Inc.) for their ability to generate a positive result in the absence of sample. This includes multiple UTM/VTM solutions, dilution of the extraction buffer components, and individual UTM/VTM components.

Results: The most important factor in UTM/VTM liquid sample dilution of the extraction buffer was ionic strength as measured by conductivity. Dilutions with conductivity below ~ 17 mS/cm induce a false positive result.

Conclusions: Evaluation of rapid antigen tests using libraries of older samples and samples collected in UTM/VTM is the most likely reason for discrepant results. The over-dilution of extraction buffer with UTM/VTM liquid samples may drive non-specific electrostatic interactions between the antibodies in the assay.