Comparison of Commercial ELISA and Rapid Tests

According to the results of a study recently published in the Journal of Infectious Diseases.

Polymerase chain reaction (PCR)-based tests have become the cornerstone of SARS-CoV-2 diagnosis; however, the diagnostic potential of the antibody test has not yet been fully evaluated. Although several ELISAs and rapid tests have become available, their diagnostic ability has not yet been carefully evaluated or compared. Therefore, to assess the potential for use in the clinical setting, this study compared the sensitivities and specificities of 4 commercial ELISA tests and 2 rapid tests in patients with symptomatic SARS-CoV-2 infection.

A total of 77 patients infected with PCR-confirmed SARS-CoV-2 were included, and the patients were classified into 3 groups based on the interval since symptom onset. Group 1 included 30 individuals whose serum/plasma samples were obtained at symptom onset or 1-5 days after symptom onset. Group 2 included 25 patients whose serum/plasma samples were obtained between days 6 and 10 after symptom onset. Group 3 included 22 patients whose serum/plasma specimens were obtained ≥ 11 days after symptom onset.

Antibodies to SARS-CoV-2 were assessed using the following serological tests: Euroimmun SARS-COV-2 IgA and IgG ELISA (Euroimmun, Germany), Wantai SARS-CoV-2 Immunoglobulin M (IgM) and antibodies total (Ab) ELISA (Beijing Wantai Biological Pharmacy Ent, China), Wantai SARS-CoV-2 Ab rapid test (China) and 2019-nCoV IgG/IgM rapid test (Hangzhou ALL Test Biotech Co., China).

Nasopharyngeal swab/breath specimens had significantly different virus concentrations between the 3 groups. The highest concentrations were in group 1, followed by group 2; the lowest concentrations were in group 3.

Test sensitivity was found to be low (<40%) within the first 5 days of symptom onset, and ELISA IgM, IgA, and total antibody sensitivity increased (>80%) 6-10 days after the onset of symptoms. All tests assessed showed positive results in all patients ≥ 11 days after symptom onset. The ELISA specificities were 83% for IgA, 98% for IgG and 97% for IgM and total antibodies.

Euroimmun-IgA and IgG ELISA tests were positive in 30% and 3.3%, respectively, of patients in group 1, and in 84% and 40%, respectively, of patients in group 2; both studies tested positive for 100% of patients in Group 3. Wantai IgM and Total Ac ELISA tests tested positive for 26.7% and 36.7%, respectively, of patients in Group 1; both tests were positive in 92% of patients in group 2 and 100% of patients in group 3. Positive results were obtained using Wantai rapid tests in 20% of patients in group 1, in 80% of patients in Group 2 and in 100% of patients in Group 3.

Positive IgM and IgG results were returned using the 2019-nCoV IgG/IgM rapid test in 20% and 13.3%, respectively, patients from group 1; in 20% and 48%, respectively, in group 2; and in 45.5% and 100%, respectively, in group 3. All results in group 1 were very weakly positive, as were the IgM positive cases in groups 2 and 3. Using 100 controls not infected with for SARS-CoV-2, specificities were 83% and 98% for Euroimmun-IgA and IgG, respectively, and 97% for Wantai IgM and Ab ELISA. The Wantai rapid test had 98% specificity and the 2019-nCOV IgG/IgM rapid test had 100% specificity for both IgM and IgG.

Overall, the study authors conclude that "although our study has the limitation of a relatively small sample size, in summary, it nevertheless provides comparative data to the first available commercial ELISA tests, indicating a high potential of the tests being evaluated for SARS-CoV-2 diagnoses, especially in symptomatic patients and advanced stages of infection."