A new test for SARS-CoV-2 antigens could determine which covid-19 patients are most likely to become critically ill.1 This test could help improve management of covid-19 by enabling hospitals to ensure that these patients have access to intensive care. While many people who develop covid-19 recover without medical intervention, roughly 20% of covid-19 patients require hospitalization and about 5% end up in the ICU, with most of those in intensive care also requiring ventilators. It is therefore imperative that hospitals set aside an adequate number of ICU beds and ventilators for these patients. In areas of the United States where most ICU beds are currently occupied, knowing which covid patients are at risk of decline could help healthcare systems to better allocate these essential resources. Identifying patients who are likely to experience severe illness is also especially crucial in low-income communities, because nearly half of these communities in the United States have no ICU beds at all. This means that clinicians in these areas need to identify patients at risk of deterioration early so that they can transfer these patients to better equipped hospitals as quickly as possible. Researchers led by David R. Walt, PhD, at Brigham and Women’s Hospital and Harvard University in Boston have now developed a test that could identify patients who are likely to need intensive care. Known as the Single Molecule Array (Simoa) SARS-CoV-2 antigen test, it is the first test that both detects and measures blood levels of S1—a protein that is part of the SARS-CoV-2 viral envelope. After developing the test, the researchers evaluated its performance in 64 patients who tested positive for covid-19 via standard diagnostic PCR testing for the virus. Of these patients, 23 had undetectable S1 concentrations, another 23 had low concentrations (6-50 pg/mL), and 18 patients had high concentrations (more than 50 pg/mL). Significantly, the researchers found a strong connection between S1 concentrations and ICU admissions. A total of 77% of the patients with high concentrations were admitted to the ICU and required intubation within 1 day of presentation at the hospital. In comparison, only 52% and 30% of patients with low and undetectable concentrations, respectively, required intensive care. “These results suggest that high S1 concentrations in plasma upon presentation to the hospital correlate with severe cases of covid-19 that can result in respiratory failure and require immediate intubation,” says Walt. “Severe covid-19 cases with acute respiratory distress syndrome can result in damage to endothelial cells and vascular leakage and we propose that this damage can lead to discharge of viral antigens into the blood.” Reference

  1. Ogata AF, Maley AM, Wu C, et al. Ultra-sensitive serial profiling of SARS-CoV-2 antigens and antibodies in plasma to understand disease progression in covid-19 patients with severe disease. Epub September 8, 2020. Clin Chem. doi:1093/clinchem/hvaa213

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 Featured image: This transmission electron microscope image shows SARS-CoV-2, the virus that causes COVID-19, isolated from a patient in the U.S. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like. Credit: NIAID-RML