Respiratory Infectious Disease

Comparison of Commercial ELISA and Rapid Tests for Diagnosis of SARS-CoV-2

Zahra Masoud
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Most HIV tests assess blood (whole, serum, or plasma) or oral fluids. Although urine-based antibody tests are also available, they are less reliable.4 Blood serum or plasma specimens have the highest sensitivity, followed by whole blood and then oral fluid specimens.2 The reason for this is twofold. First, serum or plasma specimens contain the highest concentration of HIV antigens and antibodies per unit volume.2 For example, concentrations of HIV antibodies in plasma are 300-fold higher than concentrations in oral fluids.2 Second, HIV antibodies take longer to reach detectable levels in oral secretions than in blood. In a longitudinal study of a small Nigerian cohort of people who had undergone seroconversion, the median delay between plasma and oral fluid reactivity was 29 days, which occurred regardless of viral load or HIV subtype.5

Most HIV tests assess blood (whole, serum, or plasma) or oral fluids. Although urine-based antibody tests are also available, they are less reliable.4 Blood serum or plasma specimens have the highest sensitivity, followed by whole blood and then oral fluid specimens.2 The reason for this is twofold. First, serum or plasma specimens contain the highest concentration of HIV antigens and antibodies per unit volume.2 For example, concentrations of HIV antibodies in plasma are 300-fold higher than concentrations in oral fluids.2 Second, HIV antibodies take longer to reach detectable levels in oral secretions than in blood. In a longitudinal study of a small Nigerian cohort of people who had undergone seroconversion, the median delay between plasma and oral fluid reactivity was 29 days, which occurred regardless of viral load or HIV subtype.5

A team of investigators compared the sensitivity and specificity of 4 enzyme-linked immunosorbent assays and 2 rapid tests in patients with symptomatic SARS-CoV-2 infection.

Commercially available enzyme-linked immunosorbent assay (ELISA) tests show potential for SARS-coronavirus-2 (SARS-CoV-2) diagnosis, especially in patients who have had symptoms for ≥11 days, 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 antibody test has not yet been evaluated comprehensively. Although multiple ELISA and rapid tests have become available, their diagnostic ability has yet to be thoroughly evaluated or compared. Therefore, to assess the potential for use in the clinical setting, this study compared sensitivities and specificities of 4 commercial ELISA and 2 rapid tests in patients with symptomatic SARS-CoV-2 infection.

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

Anti-SARS-CoV-2 antibodies were assessed using the following serological assays: Euroimmun SARS-COV-2 IgA and IgG ELISAs (Euroimmun, Germany), Wantai SARS-CoV-2 Immunoglobulin M (IgM) and total antibody (Ab) ELISAs (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/respiratory specimen samples were found to have significantly differing virus concentrations among the 3 groups. The highest concentrations were in Group 1, followed by Group 2; the lowest concentrations were in Group 3.

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Test sensitivities were found to be low (<40%) within the first 5 days following symptom onset, and IgM, IgA, and total antibody ELISAs increased in sensitivity (>80%) at 6 to 10 days following symptom onset. All evaluated tests showed positive results in all patients at ≥11 days following symptom onset. ELISA specificities were 83% for IgA, 98% for IgG, and 97% for IgM and total antibody. The Euroimmun-IgA and IgG ELISAs tested 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. The Wantai IgM and total Ab ELISAs tested positive in 26.7% and 36.7%, respectively, of patients in Group 1; both assays tested positive in 92% of patients in Group 2 and 100% of patients in Group 3. Positive results were returned using the 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, of patients in Group 1; in 20% and 48%, respectively, in Group 2; and in 45.5% and 100%, respectively, in Group 3. All results from Group 1 were very weakly positive, as were the positive IgM cases in Groups 2 and 3. Using 100 non-SARS-CoV-2 infected controls, specificities were 83% and 98% for the Euroimmun-IgA and IgG, respectively, and 97% for the Wantai IgM and the Ab ELISAs. The Wantai Rapid Test had a specificity of 98%, and the 2019-nCOV IgG/IgM Rapid Test had a specificity of 100% 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 nonetheless provides comparative data on the early available commercial ELISA assays, indicating a high potential of the evaluated tests for SARS-CoV-2 diagnoses, especially in symptomatic patients and progressed stages of the infection.”

Reference

Traugott M, Aberle SW, Aberle JH, et al. Performance of SARS-CoV-2 antibody assays in different stages of the infection: comparison of commercial ELISA and rapid tests [published online May 30, 2020]. J Infect Dis. doi:10.1093/infdis/jiaa305/5849070

This article originally appeared on Infectious Disease Advisor

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