The COVID-19 antibody test involves analyzing a blood sample to track how the body responds to SARS-CoV-2, the virus that causes COVID-19. Recently, healthcare professionals in China introduced a method to detect two types of antibodies—immunoglobulin M (IgM) and immunoglobulin G (IgG). It’s important to note that these antibodies typically develop 5–14 days after exposure to the virus, so early-stage detection is limited.
Interpreting the results of an antibody test requires caution. False negatives are possible during the early stages of infection. Since the test hasn’t been fully evaluated for accuracy against other viruses like influenza, it’s recommended to pair it with another diagnostic method such as the RT-PCR test for a more definitive result.
Here are four possible outcomes of a COVID-19 antibody test and what they mean:
1. IgM Negative, IgG Negative
This result indicates no current or past COVID-19 infection. However, antibodies take time to develop—at least four days after symptoms start or seven days after exposure—so the test may not detect early-stage infections. If an infection is suspected despite these results, consider taking a PCR or antigen test, or repeating the antibody test after a few days.
2. IgM Positive, IgG Negative
This suggests an infection in its early stages, meaning the individual could still be contagious. If the results seem inconsistent with the person’s symptoms (e.g., no noticeable signs of illness), it could be a false positive. In such cases, confirm the diagnosis with a PCR test or use an ELISA test, which is considered more reliable.
3. IgM Positive, IgG Positive
This result indicates that the infection is transitioning, and the individual is likely no longer contagious.
4. IgM Negative, IgG Positive
This means the person is recovering or has recovered from COVID-19 and is no longer infectious. It may also point to some level of immunity, though the duration and strength of this immunity remain uncertain. Regardless, it’s essential to continue following safety measures.
Final Thoughts
Understanding COVID-19 antibody test results isn’t always straightforward, but these tests play a significant role in identifying past infections. They’re also useful for estimating the true COVID-19 fatality rate and assessing progress toward community immunity, also known as herd immunity. Even if you’ve tested positive for antibodies, it’s still important to follow all recommended precautions to protect yourself and others.
