Why Might Rapid Diagnostic Tests Yield False Results?

Lilian Abbo, MD, chief, infection prevention & control and antibiotic stewardship, Jackson Health System, associate professor of clinical medicine, Division of Infectious Diseases, Miller School of Medicine, University of Miami, explains why diagnostic tests may yield false positives.

Interview Transcript (slightly modified for readability)

“Some of the [diagnostics] technologies are rapidly evolving, and sometimes, there are concerns [about] how valid the results we are seeing are. I don’t think that we are seeing too many false negative or false positive results with the rapid diagnostic [tests]; what we’re seeing is that, many times, we don’t know if the person is colonized or truly infected with an organism.

Now, with molecular diagnostics, we’re able to detect the genome of bacteria, and with mass spectrometry, we’re able to find pathogens that, before, we didn’t know were part of our gut microbiome. Now, we don’t know if this is a gut translocation, and this is something that is commensal but is not causing true disease, versus now these bacteria that we always thought [were] very naïve and not causing a problem, [are] now true pathogens.

You really need to look at what’s the pretest probability:

1. What are the chances of this patient having an infection?’
2. What is the best test [that] I’m going to use in my environment? (Do I take care of transplant, neonates, pediatrics? Or do I live in a community where we don’t have superbugs or travelers?)
3. What is your population? What is the probability of this test being positive, and what is the test that you’re trying to use in that context?

If you don’t have a lot of arboviruses in your area and you start just doing PCR in spinal fluid on everyone who comes through your emergency department, you’re going to start detecting things that, perhaps, are not real. That may be a contamination in the lab sample, it could be a false positive result. So, you have to be very careful in how you use the technology and how to interpret it. You have to have a certain incidence of a disease in order to find it, and you can not just apply [rapid tests] universally to everyone.”