EUA (FDA Emergency Use Authorization of Antibody Serology Tests
Learn about the significance of serology tests in mitigating Covid-19. Get information on the expected performance characteristics of serology tests in different populations.
Since the emergence of Covid-19, researchers, scientists, and doctors have been working relentlessly to find ways of tackling the virus. So far, no specific cure or vaccine against coronavirus has been approved. However, there are millions of reported recoveries across the globe. Some treatments are effective, and researchers are building on that to find a cure. Covid-19 tests have played quite a significant role in determining what treatment options are more efficient, the prevalence of the virus, and many other facts about Covid-19.
Serology tests have been used to detect the presence of coronavirus antibodies in the blood of patients. Unlike other tests for Covid 19, like where samples are collected using nasal swabs, the goal of serology tests is not to detect the presence of the virus itself. The tests are geared at uncovering the immune response of patients to coronavirus.
It is worth noting that serology tests may fail to diagnose if someone is infected with Covid-19 effectively. The reason is that the immune system may take some time to build an immune response; at this point, it may be hard to detect antibodies. If serology tests are not the best for diagnosing Covid-19 infection, what role do they play in tackling the virus?
It can help in identifying whether or not a patient’s immune system has developed a response to the virus; this information may be useful in developing a possible vaccine for the virus. More so, serology tests can help healthcare professionals to point out patients who can donate convalescent plasma to treat patients with severe cases of Covid-19.
The FDA has authorized most of the serology tests for emergency use, and clinical trials. However, they have to meet some requirements and specifications. They have their limitations and characteristics of performance, which is better termed as accuracy.
Useful information on ways to tackle the virus can be derived from serology tests. For instance, whether the presence of antibodies indicates a certain level of immunity, and how long the perceived immunity would last.
The accuracy of serology tests is measured by the sensitivity and specificity of the tests. A serology test’s sensitivity is its ability to test the presence of SARS-CoV-2 antibodies with a low number of false positives. The specificity of a serology test, on the other hand, is its ability to identify patients without SARS-CoV-2 with the lowest number of false negatives.
To determine the sensitivity of a serology test, the test’s ability to detect antibodies in the blood of Covid-19 patients should be assessed through a nucleic acid amplification test or NAAT. In partnership with CDC, BARDA, and NIH, the FDA conducted some validation studies for the sensitivity of the tests using samples from patients confirmed Covid-19 positive by a NAAT.
On the other hand, the specificity of the tests is determined by testing a large number of frozen samples. The freezing is aimed at preventing SARS-CoV-2 from spreading, which can cause the tests to show positive results but for other types of coronaviruses.
How is the sensitivity and specificity of a serology test determined? The process entails estimation. For instance, the estimates are based on 95% confidence intervals and the number of samples used to validate the accuracy of the tests.
The performance and accuracy of the serology test can also be described through their Positive and Negative Predictive values. In order to determine the Positive and Negative Predictive Values, the specificity, sensitivity, and the prevalence of patients with the antibodies are used for the calculations. After the calculations, both false positive and false negative results are to be expected.
These figures will be useful in interpreting the results of the tests on samples collected. The values help in determining the likelihood of patients getting positive results from the serology test in a given population that actually has SARS-CoV-2 antibodies. Also, it will help determine the probability of a patient receiving negative results from the tests truly not having SARS-CoV-2 antibodies.
Several false positives and false negatives can highly characterize serology tests. As such, it is vital to have other relevant information regarding the patients’ diagnostic test results and clinical history. Otherwise, too many false positives may result from the tests.
So far, the prevalence of SARS-CoV-2 antibody-positive individuals in many populations is yet to be determined. More so, there are some factors that may affect the prevalence of antibody-positive individuals. That is the duration of the virus in the populations and the efficiency of mitigation strategies for the virus.
Factors such as the rate of infections in given populations may also cause significant variance in the prevalence. The accuracy of the serology tests may be undermined if samples are collected from low prevalence populations. The information gathered from the tests cannot be used in making decisions as they are from an asymptomatic general population. With this, there will be a need to carry out subsequent tests to determine the presence of antibodies using different viral proteins.
The FDA has evaluated the performance and accuracy of different serology tests, and come up with the requirements of the tests for Emergency Use Authorization. While determining the tests’ expected performance, the FDA assumed a prevalence of 5% PPV and NPV calculations. They also conducted tons of validation studies in a bid to show the variance in the performance of the different samples from Covid-19 positive individuals used.
Since the samples demonstrated variance in performance in samples collected at different times after symptoms showed in the individuals, the FDA had to come up with criteria for settling at an expected performance. In this case, the FDA considered the results that represented the expected performance the most. Healthcare providers, labs, and other stakeholders should refer to the FDA guidelines on the expected performance of the test results in order to understand how to use and interpret the tests. The FDA also provides a calculator to help determine the estimated performance of single tests depending on the performance characteristics and prevalence of the antibodies in a given population.
Paul Singh, MHA, BA
Covid Antibody Diagnostics™
A Natures Body Wellness Corporation, Lake Mary FL 32746
Find us on Google under Antibody Diagnostics