The emergence of the COVID-19 pandemic has introduced the public to new terms like “serology.” The general assumption is that serology is used to test if someone is COVID-19 positive with an active infection, but this isn’t necessarily true. Serology tests are performed in a lab and are used to determine if the body has developed antibodies after an infection.
Let’s examine what a serology test is and why it’s necessary for research studies of SARS-CoV-2, the virus that causes COVID-19 illness, and other contagious diseases.
Serology is the scientific study of blood serum particularly regarding the body’s immune response to pathogens, or foreign invaders. It focuses on:
It’s important to understand how the immune system functions. Generally, the immune system produces antibodies when it detects the presence of foreign invaders (antigens) in the body.
Scientists and healthcare professionals use blood samples to identify diseases or to track a person's recovery from past diseases, and to determine the types and levels of antibodies and antigens in a person's system.
Research labs can use serology tests of blood samples to determine the type of antibodies present after a person has recovered from an illness or received a vaccine. The immune system produces different types of antibodies in response to different vaccines or various infections. A person's body might also develop different levels of antibodies based on the severity of their illness or based on which vaccine they received, for example.
Different types of serology tests can be performed in the research lab, including neutralization tests, hemagglutinin-inhibition tests, enzyme-linked immunosorbent assays (ELISAs), and chemiluminescence immunoassays.
In addition to using the PCR method of diagnostic testing using oral or nasal fluids to find out if people are COVID-19 positive (actively infected), it’s important to conduct serology tests after they recover to determine if they have developed antibodies against reinfection. Antibody testing is only possible through blood samples and serology studies.
A COVID-19 serology test detects the presence of antibodies in the blood in response to the SARS-CoV-2 virus. Serology tests also overcome the limitations presented by PCR-based tests. Here some key differences between blood samples (for serology tests) and nasopharyngeal samples (for PCR tests):
A positive test result on a SARS-CoV-2 antibody test indicates you were recently or previously infected with COVID-19 (whether your body exhibited symptoms or not).
Sometimes positive serology results can be wrong, resulting in a false-positive. While such scenarios are rare, this can be due to:
Note that a positive antibody test doesn’t mean you’re fully immune to the SARS-CoV-2 virus or have a lower chance of infecting other people. The presence of SARS-CoV-2 antibodies in your blood implies that you were exposed to the virus, and may have some degree of immunity against it to prevent a reinfection. It's also important to note that antibody levels in a person's system can diminish over time, reducing a person's degree of immunity against reinfection. Studies indicate that SARS-CoV-2 antibodies remain in the system between 6-8 months after infection or vaccination, which is similar to the timeline of Influenza antibodies.
Researchers use this information to trace when and where you were exposed, monitor the spread of infection in communities, and understand where undetected cases might have occurred.
A negative result implies no antibodies were detected in the sample. It could indicate:
A negative antibody test also can occur when you’ve been tested immediately after getting infected with the SARS-CoV-2 virus. This is because the body takes at least two to three weeks to develop detectable antibodies.
Serology tests are performed using blood or plasma samples. Venipuncture, whereby a vein in the arm is punctured with a needle, has been the traditional method of collecting liquid blood samples in vials or tubes.
However, venipuncture is invasive, and has some challenges. It can cause pain, anxiety, and excessive bleeding. It also requires professionals (phlebotomists) to perform the blood collection, typically in a lab or clinical setting.
These challenges and limitations have spurred researchers to embrace alternative and less invasive blood collection methods that can be performed remotely, such as microsampling.
Microsampling is the collection of small blood samples (usually 10-20 microliters of blood) from a fingerstick using either dried blood spot (DBS) or volumetric absorptive microsampling technology.
Novel specimen collection devices like the Mitra® device and the Mitra® Collection Kit have been developed to facilitate volumetric absorptive microsampling, which is especially suitable for at-home sampling or studies conducted in remote areas. Unlike traditional blood collection methods, microsampling allows remote blood collection to be performed by the study volunteers themselves, without professional assistance.
Today, scientists can send Mitra Collection Kits to study participants living in geographically diverse areas. Study participants can easily mail their samples back for analysis using the regular postal system. This remote approach to blood sample collection has proved to be effective in recent serology research studies that promote our understanding of SARS-CoV-2. Due to its recent successes as a viable sampling approach, remote microsampling is likely to be conducted in more serology research studies in the future.