Interpretation of Positive Roche Elecsys SARS-CoV-2 Antigen Test Results: Value for Clinical Decisions

Area of Science:

• Clinical diagnostics
• Infectious disease research
• Immunology

Background:

• The Elecsys SARS-CoV-2 antigen test offers high positive predictive value but can yield false-positive (FP) results.
• FP results may lead to inappropriate patient isolation and potential exposure to infectious individuals.
• Minimizing harm from FP results requires identifying at-risk clinical scenarios.

Purpose of the Study:

• To identify clinical factors associated with false-positive Elecsys SARS-CoV-2 antigen test results.
• To recommend additional testing strategies for FP results based on clinical information.
• To reduce potential harm to patients experiencing false-positive test outcomes.

Main Methods:

• Retrospective analysis of 5989 nasopharyngeal swab samples from September 2021 to October 2023.
• Positive Elecsys test results (n=302) were further evaluated using reverse transcription-polymerase chain reaction (RT-PCR).
• Clinical information was assessed for 54 samples with positive Elecsys results but no consistent COVID-19 symptoms.

Main Results:

• 37 out of 54 evaluated samples were confirmed as false-positive results.
• All FP samples exhibited Elecsys test cutoff index (COI) values close to the threshold.
• A low COI value on the Elecsys test was associated with FP results when clinical presentation was inconsistent with COVID-19.

Conclusions:

• Additional confirmatory testing is recommended when the Elecsys SARS-CoV-2 antigen test shows a low COI value.
• Clinical presentation inconsistent with COVID-19 alongside a low COI warrants further investigation.
• This approach helps to minimize the negative impact of false-positive SARS-CoV-2 antigen test results.