FDA warns of false negative COVID results, L.A. County Health Services responds

A car leaves the College of the Canyon Parking lot in Valencia after receiving a Covid 19 test on Wednesday, November 25, 2020. Dan Watson/The Signal

The Food and Drug Administration is raising concern about the accuracy of a COVID-19 test, specifically as it relates to false negative results, in limited use at Los Angeles County testing sites. 

In a notice issued Monday, the FDA said a patient could face several risks if provided with a false negative result such as “delayed or lack of supportive treatment, lack of monitoring of infected individuals and their household or other close contacts for symptoms resulting in increased risk of spread of COVID-19 within the community, or other unintended adverse events.”

The test referenced in the communication is the Curative SARS-COV-2 test that uses laboratory technology — real-time polymerase chain reaction (PCR) — that is credited with high accuracy over other types of tests such as rapid antigen. It is typically performed by collecting a throat or nasal swab. 

The notice comes as the daily positivity rate in Los Angeles County marked 20.4% Thursday, an increase from 3.8% reached on Nov. 1. This means that one in five people who are tested are carrying the virus, according to the Public Health Department. 

Curative, a San Dimas-based company focused on COVID-19 testing, provides the county with a limited number of tests for its pop-up testing sites, according to Dr. Clemens Hong, a physician with the county Department of Health Services who oversees countywide COVID-19 testing. 

“L.A. County Department of Health Services is aware of the alert from the FDA about the risk of false negative results with Curative COVID-19 PCR tests and we are reviewing and assessing results from clinical studies,” she said in an emailed statement Thursday. 

No test is perfect, according to Dr. Bud Lawrence, medical director of Henry Mayo’s Emergency Department, adding that a lot of false negatives are usually related to poor sampling. 

“I think what the FDA is trying to say is, ‘Hey listen, this test came with instructions and maybe some people weren’t following the instructions properly.’ That is more indicative of quality control at the individual testing sites, and not necessarily indicative of the test itself not functioning properly.”

Hong reiterated that there has always been a risk of false negative results with any PCR molecular test due to how well samples are collected. All tests face similar issues because there is “no reliable way” to detect early infection or late disease. 

“This means that even if you test negative, it is still important to take steps to protect yourself and complete your quarantine for the full 14-day period (or 10 days after symptoms) because you may still be infected,” she added. “Through the county’s result notification process, we remind residents of the risk of false negatives and encourage all individuals to continue to quarantine and take precautions through the potential infectious period, even when the test is negative.”

Curative officials said in an emailed statement Thursday that its test, which received emergency use authorization, is labeled with specific warnings, precautions and limitations — recommendations the FDA said in its memo are important to reduce the risk of false negative results. 

“Regarding the FDA safety communication noting the risk of false results with the Curative SARS-CoV-2 test, we are confident in our data and we are working with the FDA closely on the matter. Testing sensitivity and accuracy on behalf of our patients is at the heart of our work,” said CEO and co-founder Fred Turner.

The FDA further recommended that health care providers consider retesting patients using a different test if they suspect inaccuracy and that patients and caregivers talk to their providers if they have concerns about their test results. 

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