FDA authorizes new Covid-19 antibody test that quantifies specific levels of antibodies

The US Food and Drug Administration has issued an emergency use authorization for Kantaro Bioscience’s Covid-19 antibody test kit, the group announced on Wednesday. The newly authorized antibody test, called COVID-SeroKlir, identifies and measures precise levels of antibodies that are present in a person after Covid-19 recovery.

The FDA confirmed to CNN on Wednesday that the agency had authorized the test. But this is not the first test to estimate a patient’s antibodies from a past coronavirus infection. The FDA previously authorized similar tests over the summer.

“Being able to measure a patient’s relative level of antibodies in response to a previous SARS-CoV-2 infection may be useful as we continue to learn more about the virus and what the existence of antibodies may mean,” Dr. Tim Stenzel, director of the Office of In Vitro Diagnostics and Radiological Health in the FDA’s Center for Devices and Radiological Health, said in a news release in July around the time the tests were authorized.

“There are still many unknowns about what the presence of SARS-CoV-2 antibodies may tell us about potential immunity,” Stenzel said at the time. “Patients should not interpret results as telling them they are immune, or have any level of immunity, from the virus.”

Kantaro Biosciences — a joint venture between Mount Sinai and RenalytixAI to scale up innovation and testing efforts — announced on Wednesday that it has partnered with Bio-Techne Corporation to manufacture its testing kits with an initial capacity of up to 10 million tests per month.

While the newly authorized Covid-19 antibody test is similar to others in that it detects Covid-19 antibody levels, it takes testing a step further by providing a number readout of the level detected — and not just a simple positive or negative result, said Dr. Amesh Adalja, senior scholar at the Johns Hopkins University Center for Health Security, who was not involved in the Kantaro test.

“The ability to quantify what the antibody levels are helps us understand what level of antibody is correlated with being protected from infection,” Adalja told CNN on Wednesday.

“Every test is going to have a limit of detection — meaning the test is going to have a limit where they have some level of antibodies that have to be present for the test to be positive, and when it’s below that, the test will be negative,” Adalja said. “My understanding of this test is that it actually gives you a number so that you can say your antibody titer is X, Y or Z.”

This type of data on antibody levels could help inform vaccine development, Adalja said.

“I also think that becomes important when we think about the vaccine, because we will often sometimes vaccinate someone and will want to know the levels of antibody that are generated and then follow those people over time to understand what the interval might be for boosting them,” Adalja said. “So if the antibodies fall below a certain level after three years, then you can get a booster at three years.”

Studies suggest that Covid-19 antibody levels can dwindle over time — after a period of about five to six months — but more research is needed, said Dr. Saju Mathew, an Atlanta-based primary care physician and public health specialist, who was not involved in the newly authorized Kantaro test.

“So a test like this would be exciting if it is accurate,” Mathew told CNN on Wednesday.

“This test is suggesting that it’s greater than 98% sensitive and specific, which is good,” Mathew added, referencing Kantaro’s announcement that the test has demonstrated 98.8% sensitivity and 99.6% specificity for detecting novel coronavirus antibodies against two virus antigens.

“It looks at two viral antigens, including the spike protein,” Mathew said.

“The spike protein is the protein that the virus uses to get into our lungs and infect the body. So that’s why I think that this test definitely holds some promise,” Mathew said. “Ultimately the end game is, how accurate is this test?”

Mathew added that patients must keep in mind this is a test for detecting antibodies, which suggest having a previous Covid-19 infection — not a current one. Mathew also emphasized that having antibodies does not mean someone is immune to Covid-19 for a lifetime, but perhaps they have some protection for weeks or months.