False-negative COVID-19 tests may lead to a "second wave of infection"

A special report from the Mayo Clinic warns that health care providers and officials must be aware of the limitations of reverse transcriptase-polymerase chain reaction (RT-PCR) testing and the potential for false negatives. 

The article emphasizes that clinical and public health decisions should not be heavily reliant on the results of COVID-19 tests. The experts suggest that RT-PCR testing is accurate in diagnosing infection, but not as reliable in ruling it out. 

Study co-author Dr. Priya Sampathkumar is an infectious diseases specialist at the Mayo Clinic.

“RT-PCR testing is most useful when it is positive. It is less useful in ruling out COVID-19. A negative test often does not mean the person does not have the disease, and test results need to be considered in the context of patient characteristics and exposure,” explains Dr. Sampathkumar.

Previously, the National Institutes of Health (NIH) conducted a study based on more than 600 patients who were hospitalized for COVID-19 in Wuhan during February. The experts discovered a “potentially high false negative rate of real-time RT-PCR testing for SARS-CoV-2.” In some cases, RT-PCR results were variable for the same patients over the course of diagnosis and treatment. 

The Mayo Clinic warns that overreliance on COVID-19 test results can have a negative impact on efforts to control the pandemic. Dr. Sampathkumar says that health care officials should expect a “less visible second wave of infection from people with false-negative test results.”

Even with an accuracy rate as high as 90 percent, the risk of false negatives will grow as more people are tested.

“In California, estimates say the rate of COVID-19 infection may exceed 50% by mid-May 2020. With a population of 40 million people, 2 million false-negative results would be expected in California with comprehensive testing. Even if only 1% of the population was tested, 20,000 false-negative results would be expected.”

The Mayo Clinic recommends for public health officials to use evidence-based reasoning while dealing with the COVID-19 pandemic. The experts say risk levels must be carefully assessed prior to testing, and negative test results should be viewed cautiously, especially for people in high-risk categories and in areas where COVID-19 infection is widespread.

“For truly low-risk individuals, negative test results may be sufficiently reassuring,” explains study first author Dr. Colin West. “For higher-risk individuals, even those without symptoms, the risk of false-negative test results requires additional measures to protect against the spread of disease, such as extended self-isolation.”

“We need to continue to refine protocols for asymptomatic patients and exposed health care workers,” says Dr. Sampathkumar.

The report is published in Mayo Clinic Proceedings.

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By Chrissy Sexton, Earth.com Staff Writer