CONTINUING EDUCATION :: ANTIBODIES
Figure 1. Antibody responses over time a
https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(21)00221-4/fulltext The presented figure is a simplified representation to increase general understanding but can be variable for different individuals in different settings. For example, some individuals exhibit RNA levels that can stay elevated for weeks to months following disease resolution. Adapted from Ong D, et al. Clin Microbiol Infect. 2021;27(7):981-986. doi: 10.1016/
j.cmi.2021.05.001, with permission from Elsevier #5167800710801.
lectively, these findings suggest that an antibody response to SARS-CoV-2 plays an important role in modulating COVID- 19 disease.
Current FDA EUA offering for SARS-CoV-2 Ab assays The U.S. Food and Drug Administration (FDA) performed independent studies to evaluate the clinical performance of SARS-CoV-2 Ab tests. These studies resulted in the withdrawal or amend- ment of the emergency use authoriza- tion (EUA) for several tests because the assays’ clinical performance did not meet FDA requirements. False positives can result from cross reactivity with preex- isting antibodies from previous infection with other coronaviruses that cause the common cold (229E, NL62, OC43, and HKU1), SARS-CoV, or MERS-CoV, as well as with antibody tests with low specific- ity.19
Negative results may also occur in
SARS-CoV-2 infected individuals due to lack of antibody production in the early stages of infection, and thus, making serology tests not suitable for diagnosis of infection.19,20 All SARS-CoV-2 Ab tests that are currently authorized by the FDA under EUA are intended to aid in the detection of recent or past infection indicating an adaptive immune response.21
A compre-
hensive list of serology tests that have been granted EUA can be found on the FDA website. Two different types of serology tests
have been granted EUA, binding anti- body tests and neutralizing antibody
Figure 2. RBD-Specific Antibody Titers as a Surrogate of Neutralization Potency in Acutely Infected COVID-19 Patients
Reprinted from Suthar M, et al. Neutralizing Antibody Responses in COVID-19 Patients. Cell Rep Med. 2020 Jun 23;1(3):100040. doi: 10.1016/j.xcrm.2020.100040, with permission from Elsevier. # 5167770944099
MLO-ONLINE.COM DECEMBER 2021 9 (nAb) tests.22 Binding antibody tests
detect the presence of antibodies to the SARS-CoV-2 virus, but the antibodies detected are not necessarily capable of conferring immunity.22
Binding antibody
tests employ several different types of assay methodologies, including lateral flow (LF), microfluidic immunoassay, chemiluminescence (CIA), and enzyme linked immunosorbent assay (ELISA). LF and microfluidic methods are rapid, compact, portable, easy to use, and typi- cally require only a small amount of blood
(fingerstick), serum, or plasma. Results are generally reported qualitatively. These tests lend themselves well for use in the field or at the point of care by non- laboratory medical staff. However, the performance characteristics (especially sensitivity) differ among many LF and microfluidic immunoassays. CIA and ELISA methods are laborato- ry-based methods best suited for the high throughput setting of the central labo- ratory. Results can be reported qualita- tively, semi-quantitatively, or quantitively,
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