A report from the University Hospital of Basel, recently published by The Lancet, adds to evidence of the unreliability of PCR and antibody Covid-19 tests.
An 81 year old woman with Covid-19 symptoms was admitted to the hospital and given a SARS-CoV-2 PCR test1. The test came back negative. 6 weeks later she was given an antibody test2. The antibody test also came back negative.
However, two days after admission, a skin sample from an area with a rash was taken from the woman and tested using a skin PCR test. This test came back positive.
The report’s authors say the case is important because it highlights the shortcomings of currently available testing methods for SARS-CoV-2 infection, both PCR and antibody tests.
In addition, the lack of antibodies in the blood after 6 weeks suggests that some patients with COVID-19 might not establish humoral immunity, something observed with other coronaviruses.
Humoral immunity refers an immune response detected in fluids outside cells, such as antibodies. Another kind of immunity known as cell-mediated immunity is an immune response that does not involve antibodies. This includes T-cell and B-cell responses that are not detected by antibody tests.
The authors also suggest that Covid-19 skin tests might be used in addition to regular PCR and antibody tests for diagnosing patients and for determining how many people have been infected.
1 Nasopharyngeal swab, Cobas SARS-CoV-2 Test, Roche Diagnostics.
2 Elecsys Anti-SARS-CoV-2, Roche Diagnostics.
Lancet publication (in English)