key: cord-0695455-4zi9h7ct
authors: García‐Salguero, Cristina; Culebras, Esther; Merino, Paloma; Baos, Elvira; Delgado‐Iribarren, Alberto
title: Usefulness of SARS‐CoV‐2 antigen test sample as input for SARS‐CoV‐2 RT‐PCR analysis
date: 2021-11-22
journal: J Med Virol
DOI: 10.1002/jmv.27459
sha: 9be33d238114659fa873431fd2955b3ca10fa45c
doc_id: 695455
cord_uid: 4zi9h7ct

SARS‐CoV‐2 rapid detection is of great interest to prevent viral dissemination. In that sense, antigen tests appeared as a very valuable tool to reach this goal. However, it is possible to obtain a negative result in those patients with low viral loads, and consequently, reverse transcription‐polymerase chain reaction (RT‐PCR) should be performed on samples from patients with a negative antigen test in which there is a strong suspicion of COVID infection. The common diagnostic algorithm involves taking a second sample for RT‐PCR testing. This study evaluates the usefulness of the antigen test sample for carrying out RT‐PCR analysis when necessary. Results obtained indicate that can be used a unique sample for both antigen test and RT‐PCR. This data showed that it is possible to reduce excessive suspected individuals managing and so on increase staff security and patient comfort.

The SARS-CoV-2 pandemic has generated a great demand for useful and rapid tools for the diagnosis of this virus. 1 Although real-time reverse transcription-polymerase chain reaction (RT-PCR) is the technique considered the reference laboratory method to diagnose SARS-CoV-2 infection, 2 other tests such as rapid antigen (Ag) detection tests have been developed and many have received regulatory approval. 3 Also, these devices have been used to perform a rapid screening, thus avoiding the performance of RT-PCR, a much more laborious, expensive, and timeconsuming technique, to those samples that give a positive result. 4, 5 Some studies 6 have shown a sensitivity of these devices that ranges from 90% to 95%, when the patient's viral load is high, cycle threshold (C t ) value < 30, to a sensitivity of 10%-40% when the viral load is low, C t value ≥ 30. C t values cannot be used to determine viral load or infectivity in an individual, but there is an inverse relationship between C t value and the amount of genetic material present in specimens. 7 Therefore, all negative results must be verified using another technique in those patients deemed necessary.

Until now, the most widely used sample for the diagnosis of COVID-19 is the nasopharyngeal swab. The collection of this sample, although is not painful, is very unpleasant and irritating for the patient and represents a risk for the spread of the virus as respiratory secretions are the main route of infection. 8 Therefore, to avoid patient discomfort as well as a duplicate exposure of the healthcare personnel, the objective of this study has been to study the possibility of using a single nasopharyngeal swab to perform both the Ag test and RT-PCR analysis when it is considered necessary. 

Considerations for diagnostic COVID-19 test

Detection of SARS-CoV-2 in different types of clinical specimens

IFCC interim guidelines on rapid point-of-care antigen testing for SARS-CoV-2 detection in asymptomatic and symptomatic individuals

Evaluation of SARS-CoV-2 rapid antigen test in pediatric population

Comparative diagnostic performance of different rapid antigen detection test for COVID-19 in the real-world hospital setting

Evaluation of three rapid lateral flow antigen detection tests for the diagnosis of SARS-CoV-2 infection

Antigen Card test relative to the severe acute respiratory coronavirus virus 2 (SARS-CoV-2) real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay among symptomatic and asymptomatic healthcare employees

Comparison of saliva with oral and nasopharyngeal swabs for SARS-CoV-2 detection on various commercial and laboratory developed assays

Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection

Diagnostic performance of CerTest and Panbio antigen rapid diagnostic tests to diagnose SARS-CoV-2 infection

The authors confirm that the main data supporting the findings of this study are available within the manuscript. Any additional information is available on request from the corresponding author (CGS).