Association between viral load and positivization time of a SARS-CoV-2 rapid antigen test in routine nasopharyngeal specimens

Viral load and time to rapid SARS-CoV-2 antigen test positivization

  • Prof. Gian Luca Salvagno Section of Clinical Biochemistry, University of Verona, Verona, Italy & Service of Laboratory Medicine, Pederzoli Hospital, Peschiera del Garda, Italy
  • Dr. Brandon Michael Henry Clinical Laboratory, Division of Nephrology and Hypertension, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA & Disease Intervention & Prevention and Population Health Programs, Texas Biomedical Research Institute, San Antonio, Texas, USA
  • Dr. Simone De Nitto Section of Clinical Biochemistry, University of Verona, Verona, Italy & Service of Laboratory Medicine, Pederzoli Hospital, Peschiera del Garda, Italy
  • Dr. Laura Pighi Section of Clinical Biochemistry, University of Verona, Verona, Italy & Service of Laboratory Medicine, Pederzoli Hospital, Peschiera del Garda, Italy
  • Prof. Giuseppe Lippi
DOI: https://doi.org/10.5937/jomb0-35482
Keywords: COVID-19, SARS-CoV-2, Laboratory Medicine, Diagnosis, Immunoassay

Abstract


Background: Rapid SARS-CoV-2 antigen tests are potentially useful tools for screening carriers with high viral load. This study was aimed to assess the potential association between viral load and positivization time of a manual SARS-CoV-2 commercial antigen test in routine nasopharyngeal specimens.

Methods: In a sample of subjects undergoing routine diagnostic testing, SARS-CoV-2 positivity of nasopharyngeal samples was assayed with both molecular (Altona Diagnostics RealStar SARS-CoV-2 RT-PCR Kit) and antigenic (Roche SARS-CoV-2 Rapid Antigen Test) tests. Positivization time of rapid antigen test was correlated and compared with viral load expressed as mean of SARS-CoV-2 E/S genes cycle threshold (Ct) values.

Results: The study sample consisted of 106 patients (median age 48 years, 55 women) with positive results of rapid SARS-CoV-2 antigen testing. A highly significant Spearman’s correlation was found between mean SARS-CoV-2 E/S genes Ct values and positivization time of manual antigen test (r= 0.70; p<0.001). The positivization time of rapid SARS-CoV-2 antigen test displayed an area under the curve of 0.82 (95%CI, 0.74-0.89) for predicting nasopharyngeal samples with high viral load (i.e., mean Ct <20). A positivization time cut-off of 32 sec had 94.9% sensitivity and 58.2% specificity for detecting specimens with high viral load. The overall agreement between mean Ct value <20 and positivization time <32 sec was 70.8%.

Conclusions: Positivization time of rapid SARS-CoV-2 antigen tests may provide easy and rapid information on viral load, thus making this type of manual assay potentially suitable for quick and reliable detection and isolation of super-carries.

 

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Published
2022/01/28
Issue
Vol. 41 No. 4 (2022): Journal of Medical Biochemistry
Section
Short Communication

Copyright (c) 2022 Brandon Michael Henry, Laura Pighi, Simone De Nitto, Gian Luca Salvagno, Giuseppe Lippi

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