Image of microscopic view of SARS-CoV2 neutralizing antibodies.

ARUP experts evaluated an Emergency Use Authorization assay that detects SARS-CoV-2 neutralizing antibodies such as those pictured.

July 19, 2021

A new antibody test that has earned Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) effectively detects SARS-CoV-2 neutralizing antibodies (nAbs), according to an analysis recently published in the Archives of Pathology and Laboratory Medicine by experts at ARUP Laboratories. Because evidence indicates a correlation between nAbs and protective immunity against SARS-CoV-2, the GenScript cPass neutralization antibody assay may play an important role in helping researchers understand long-term immunity against COVID-19.

“As the pandemic evolves with increasing vaccination rates and the circulation of new variants, research that advances our understanding of COVID-19 protective immunity becomes increasingly important,” said Julio Delgado, MD, MS, executive vice president of ARUP Laboratories and chief of the Division of Clinical Pathology at the University of Utah. “Serology assays like this are key to this understanding,”

ARUP authors, in collaboration with researchers from the University of Utah and Brigham Young University (BYU), evaluated the GenScript-developed cPass assay and compared it with commercially available COVID-19 total IgG serology assays, which detect all IgG binding antibodies and cannot differentiate between nAbs and other antibodies.

“At this time, neutralizing antibodies are the only markers that have been shown to correlate directly with protection,” said Vijayalakshmi Nandakumar, PhD, MS, medical director of Immunology at ARUP and assistant professor of clinical pathology at the University of Utah. “However, there aren’t many assays that can specifically detect these antibodies. In fact, due to biosafety concerns, the gold standard assay can only be performed in select laboratories.”

The standard assay measures the ability of antibodies to block the growth of live SARS-CoV-2 virus. Because active virus is required to perform the test, only laboratories with a high biosafety rating (biosafety level 3) can safely perform it. In contrast, the GenScript cPass neutralization antibody assay can be performed safely in most laboratories because it relies on an inactive surrogate particle that mimics the SARS-CoV-2 receptor binding domain.

“Neutralizing antibodies block the virus’s ability to infect a host, and their presence has been correlated with protective immunity. Our goal was to analyze the cPass assay’s ability to detect neutralizing antibodies to understand its role in the study of SARS-CoV-2 immunity,” Nandakumar explained.

“Our research supports the use of the cPass assay to accurately detect nAb response. We also found that positive total IgG results from commercial assays correlate with the presence of nAbs, suggesting that these assays may serve as a substitute when nAb-specific assays are not available,” Nandakumar said. “This is great news because most laboratories already perform these total IgG assays.”

ARUP offers several total IgG serology assays that detect antibodies that form due to vaccination or natural infection. “We continue to monitor and study the ongoing COVID-19 situation and are continuously evaluating our test offerings to best serve the community,” Delgado concluded.


Kirsten Meek, PhD,