One study shows the rapid test is not very sensitive.
The gold standard is a quantitative polymerase chain reaction (qPCR)-based system taking several hours to confirm positivity. For effective public health containment measures, this time span is too long. We therefore evaluated a rapid test in a high-prevalence community setting.
Of 49 individuals, 22 tested positive by repeated qPCR. In contrast, the rapid test detected only eight of those positive correctly (sensitivity: 36.4%). Of the 27 qPCR-negative individuals, 24 were detected correctly (specificity: 88.9%).
Döhla M, Boesecke C, Schulte B, et al. Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity. Public Health. 2020;182:170-172. doi:10.1016/j.puhe.2020.04.009 https://pubmed.ncbi.nlm.nih.gov/32334183/
Below: Serum test sensitivity range from 34% to 92%, a huge range, indicating an inaccuracy for this type of test.
“The reverse transcription‐quantitative real‐time polymerase chain reaction (RT‐qPCR) assay has become the primary and crucial diagnostic tool to identify the SARS‐CoV‐2 infection, but it has some limitations in clinical practice. The RNA‐based diagnostic tests show a positive result only when the virus is still present. The tests cannot identify the people who were previously infected, recovered, and have cleared the virus from their bodies. A total of 76 serum samples, collected from these patients during hospitalization, were tested for IgM and IgG antibodies against SARS‐CoV‐2. The total seropositive rate for IgM and IgG was 50.0% (19/38) and 92.1% (35/38), respectively.”
Perchetti GA, Nalla AK, Huang ML, et al. Validation of SARS-CoV-2 detection across multiple specimen types. J Clin Virol. 2020;128:104438. doi:10.1016/j.jcv.2020.104438 https://onlinelibrary.wiley.com/doi/full/10.1002/jmv.25919
Below is a table from the above study. Variables include location in body of the sample source, and days since symptoms.
Below are some comments from a meta study that looked at many other studies about testing for SARS-COV-2.
In the study below they found many problems with the tests, one problem being, a lack of studies where people had no symptoms, to compare to a sample of people who had symptoms and are not in the hospital.
Pooled results for IgG, IgM, IgA, total antibodies and IgG/IgM all showed low sensitivity during the first week since onset of symptoms (all less than 30.1%), rising in the second week and reaching their highest values in the third week. The combination of IgG/IgM had a sensitivity of 30.1% (95% CI 21.4 to 40.7) for 1 to 7 days, 72.2% (95% CI 63.5 to 79.5) for 8 to 14 days, 91.4% (95% CI 87.0 to 94.4) for 15 to 21 days.
The sensitivity of antibody tests is too low in the first week since symptom onset to have a primary role for the diagnosis of COVID-19, but they may still have a role complementing other testing in individuals presenting later, when RT-PCR tests are negative, or are not done. Antibody tests are likely to have a useful role for detecting previous SARS-CoV-2 infection if used 15 or more days after the onset of symptoms.”
Sensitivity has mainly been evaluated in hospitalised patients, so it is unclear whether the tests are able to detect lower antibody levels likely seen with milder and asymptomatic COVID-19 disease.
Deeks JJ, Dinnes J, Takwoingi Y, et al. Antibody tests for identification of current and past infection with SARS-CoV-2. Cochrane Database Syst Rev. 2020;6:CD013652. Published 2020 Jun 25. doi:10.1002/14651858.CD013652 https://pubmed.ncbi.nlm.nih.gov/32584464/
