Three Common SARS-CoV-2 Antibody Testing Myths Debunked
It can be hard to decipher fact from fiction when it comes to COVID-19. Here are three myths debunked surrounding SARS-CoV-2 antibody testing.
- Antibody testing will tell me exactly when I was infected
- If I take a PCR test (a diagnostic test that looks for an active coronavirus infection), I do not need to take an antibody test
- Antibody tests are not accurate
False—however, an IgM assay will provide information about current or recent infection; while a separate IgG assay in addition will also give information about a more sustainable immune response.1
Testing for IgM and IgG separately may be better than one combined test, as seroconversion is an individualized journey.2
If a patient takes one antibody test (that tests for both IgG and IgM antibodies together), and the test comes back positive, the clinician does not know if the patient has been more recently infected or has an immune response to a prior infection.
This is because, generally, IgM is the first antibody developed against an antigen and is detectable earlier, while IgG is developed later after the infection occurs and can be detectable for months and/or years, depending upon the antigen and the individual.3
False—while it is important to take a PCR test if you believe you have an active infection, studies are showing a high false-negative rate of real‐time reverse transcription‐polymerase chain reaction (RT‐PCR) results for SARS‐CoV‐2 detection.4 In fact, a recent Johns Hopkins study found that the possibility of a false-negative from the PCR test is greater than one in five— and at times far higher.5 This study concluded, "If clinical suspicion is high, infection should not be ruled out on the basis of RT-PCR alone."6
Therefore, complementing PCR testing with IgM testing can provide greater clarity into patient status.7
False—however, not all antibody tests are made the same. It’s important to ensure your antibody tests have high specificity and sensitivity to minimize false-positive results.8 Sensitivity refers to the test’s ability to correctly identify patients with COVID-19 antibodies, and specificity refers to the test’s ability to correctly identify patients without COVID-19 antibodies – it’s important to have both high sensitivity and high specificity in a test.
Testing for IgM and IgG separately may provide physician’s more clarity into patient status when compared to one combined test, as seroconversion is an individualized journey.4
Beckman Coulter’s IgM SARS-CoV-2 test has a specificity of 99.9% and a sensitivity of 15-30 days POS 98.3%; Beckman Coulter’s IgG SARS-CoV-2 test has a specificity of 99.6% and a sensitivity of >18 days 100% (75.8% <7 days).