Current best evidence for clinical care (more info)
We aimed to evaluate the LIAISON® SARS-CoV-2 antigen assay (DiaSorin), comparing its performance to real-time polymerase chain reaction (RT-PCR) for the detection of SARS-CoV-2 RNA. 182 (110 PCR-positive and 72 PCR-negative) nasopharyngeal swab samples were taken for the detection of SARS-CoV-2. RT-PCR and antigen assay were performed using the same material. The sensitivity and specificity of the antigen assay were calculated for different cut-offs, with RT-PCR serving as the reference method. Stored clinical samples that were positive for other respiratory viruses were tested to evaluate cross-reactivity. One third (33/110, 30%) were falsely classified as negative, while no false positives were found using the 200 TCID50/mL cut-off for the SARS-CoV-2 antigen as proposed by the manufacturer. This corresponded to a sensitivity of 70% (60-78%) and a specificity of 100% (94-100%). Lowering the cut-off for positivity of the antigen assay to 22.79 or 57.68 TCID50/mL increased the sensitivity of the method, reaching a sensitivity of 92% (85-96%) vs. 79% (70-86%) and a specificity of 81% (69-89%) vs. 99% (91-100%), respectively. The antigen assay reliably detected samples with high SARS-CoV-2 viral loads (=106 copies SARS-CoV-2/mL), while it cannot differentiate between negative and low positive samples. Cross-reactivity toward other respiratory viruses was not detected.
| Discipline / Specialty Area | Score |
|---|---|
| Public Health | |
| Hospital Doctor/Hospitalists | |
| Internal Medicine | |
| Infectious Disease | |
This study looks at the sensitivity and specificity of a commercially available SARS-CoV-2 antigen test compared with the gold standard RT-PCR. The test did well in high-titer specimens, less well in low-titer specimens. This paper is similar to another one recently published using the same assay: https://doi.org/10.1128/JCM.00374-21.
Antigen-based tests are not as sensitive as PCR-based tests. That is, they miss more infected people than PCR-based tests. The purpose of testing is to identify infected people and thereby avoid spread of the virus, that is, to NOT miss infected people. Therefore, situations in which antigen-based testing is indicated are limited.