“How we treat patients is going to depend on understanding this concept,” Metlay told Medscape Medical News. “It isn’t one number. It’s actually much more complicated and very nuanced.” If clinicians don’t understand that, he added, “We’re really going to make mistakes about how to use all these negative tests.”
When Hope Outstrips Reason
A positive SARS-CoV-2 test sets off a cascade of actions, in and out of clinical settings: In patients with symptoms, it triggers a set of protocols, as recommended by the National Institutes of Health��and individual hospitals, around use of personal protective equipment (PPE) for staff, whether patients are placed in rooms with others or singly, and specific treatment choices, such as which ventilator protocol to use. By contrast, a negative test, in an ideal situation, should lead a clinician to keep looking for a causative agent or underlying problem. Quality care, in other words, relies on accurate diagnosis.
In patients without symptoms, a positive test means suggesting quarantine and isolation for two weeks, said Colin West, MD, PhD, professor of medicine and biostatistics at the Mayo Clinic in Rochester, Minnesota.
But because of the relatively high rate of false negatives, a negative test in an asymptomatic person can’t confer the kind of relief patients, the public, or policymakers would like it to, West said.
“People can’t relax their physical distancing, their handwashing, their surface hygiene, their mask-wearing” even with a negative test, he said, because they still could be carrying the virus.
“When hope outstrips reason, we sometimes prematurely pin our hopes on tests that aren’t as good as we want them to be,” said West, who wrote a perspective for Mayo Clinic Proceedings warning about the dangers of false negatives. “Smart clinicians all around the country are not believing the test results when their clinical suspicion is high enough.”
Calculating Clinical Suspicion
With false negative rates ranging from 3.2% in a cohort of seriously ill COVID-19 inpatients in New York City, to 66% in the mixed population in the Annals of Internal Medicine study, it’s understandable that clinicians might be skeptical of the results in front of them.
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