Internationally standardized respiratory viral load testing with limited resources: A derivative‐of‐care calibration strategy for SARS‐CoV‐2

Abstract

IntroductionSARS‐CoV‐2 has demonstrated that, in targeted circumstances, viral quantification within respiratory specimens can valuably inform patient management, as well as research. Nevertheless, the pandemic has illustrated concomitant challenges for obtaining high‐quality (and broadly comparable) respiratory viral loads. This includes a critical need for standardization and calibration, even though the necessary resources may not always be available for emergent pathogens and non‐bloodstream specimens.MethodsTo these ends, we describe a novel strategy for implementing quantitative SARS‐CoV‐2 testing with International Unit‐based calibration. Earlier in the course of the pandemic—when analytic resources were far more limited—select residual SARS‐CoV‐2 positive specimens from routine care in our diagnostic laboratory were pooled to formulate a clinically realistic secondary standard of high volume and analyte concentration, which was cross‐calibrated to the primary SARS‐CoV‐2 standard of the World Health Organization.ResultsThe resultant calibrators were integrated into the original CDC RT‐qPCR assay for SARS‐CoV‐2, whose (now broadened) performance characteristics were defined to generate a test appropriate for both clinical and research use. This test allowed for the quantification of virus in respiratory specimens down to a validated lower limit of quantification of 103.4 IU/ml.ConclusionsBy self‐formulating calibrators from this derivative‐of‐care secondary standard, we successfully validated respiratory viral loads without the commercial availability (at that time) of quantitative assays or calibrators. As the SARS‐CoV‐2 pandemic continues to decline—and even beyond this pathogen—this strategy may be applicable for laboratories seeking to implement viral load testing for nontraditional specimen types despite limited resources.