FDA has issued a safety communication about the risk of false results when using startup Curative's test for COVID-19, which is used by the U.S. Air Force and cities including Seattle and Los Angeles, where Curative reportedly processes 35,000 samples a day.
After learning of false results, particularly false negatives, associated with the PCR test, FDA reiterated the need to use Curative's kit in accordance with its label and instructions. FDA highlighted the need to test people within 14 days of symptom onset.
- FDA's safety communication lacks information about the rate of false negatives or an explanation for why the test may be delivering erroneous results. Los Angeles-based Curative was founded in January 2020 to focus on sepsis but has pivoted to COVID-19. Justin Mateen, founder of dating app Tinder, is its lead investor, according to Crunchbase.
FDA’s safety communication lacks information about the rate of false negatives or an explanation for why the test may be delivering erroneous results. However, the recommendations highlighted by FDA point to possible explanations for the false negatives.
The agency picked out two points from the label for Curative’s test in its recommendations for the proper use of the product. Specifically, FDA said tests should only be performed on symptomatic people who first developed signs of COVID-19 in the past 14 days. Accuracy in people who are asymptomatic or developed symptoms more than 14 days ago may be reduced due to their lower viral loads.
The second point highlighted by FDA addresses the need for a trained healthcare worker to directly observe and direct the collection of samples. Studies have identified poor nasopharyngeal swabbing techniques as a potential cause of false negatives in community testing locations. Curative's test is cleared for use with nasopharyngeal samples, as well as nasal and throat swabs, but its community testing partners typically take oral swabs.
There is little information on the ability of patients at community testing centers to adhere to the instructions for taking oral swabs. Patients cannot eat, drink, smoke or use mouthwash in the 20 minutes prior and need to cough deeply three times to bring up the saliva required for the test. The swab must then be run around the inside of the mouth, touching inside each cheek, the gums, the tongue and the roof, for at least 20 seconds.
If a patient fails to follow those instructions, the swab may lack sufficient sample to detect the virus. FDA’s focus on the need for healthcare providers to oversee the process suggests that theoretical risk may be a potential factor in the false negatives. Curative is working with FDA to resolve the matter.
"Today, the FDA issued a warning of 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. Curative will be providing additional updates and information soon," Curative CEO Fred Turner said in a statement.
FDA's statement makes no reference of the potential for false negatives to occur on the day COVID-19 symptoms develop. However, a pooled analysis of studies of other PCR tests found the false negative rate fell from 38% on the day symptoms started to 20% three days later.