By Marti Webb Slay
With the increase of PCR testing during the COVID pandemic, the use of PCR tests vs. antigen tests vs. cultures is being reexamined, with questions about the balance between speed and accuracy, and which tests are reimbursed by insurance and which are not.
Dan Carter, MD, pediatrician and lab medical director at Greenvale Pediatrics Hoover, is watching the debates about the options and when to order which type of test in the changing landscape.
For UTI infections, for instance, cultures are still the gold standard and the only test most insurance plans cover. “With a culture, within about five days you know exactly what bacteria it is and the antibiotics that work effectively against it,” he said. “But a PCR test looks at the genetic makeup of the bacteria, and based on the history of that genetic makeup, they are able to determine what its sensitivities will be and what its characteristics are. It’s not a better test; it’s a much faster test. The time difference is between several days for a culture to grow and receiving PCR results within about 12 hours. That can be critical for the very young and very old with a UTI.”
Very few insurance plans cover PCR testing for UTI infections, however. “It’s controversial, because when you are testing the old-fashioned way, there is never a false result,” Carter said. “Using genetics to test is trickier. They make assumptions that because the genetic material matches a certain bacteria, it’s going to have certain characteristic in how it relates to antibiotics.”
Carter likens PCR tests to fingerprints. The doctor has to know what bacteria to test for. If a UTI is caused by e. coli, a common culprit, a physician can test for that and proceed with treatment quickly. If the UTI is caused by a less common bacteria, it may not show up on the requested PCR tests.
Carter said that uncertainty is scary to physicians and insurance companies, and the nephrology community has not been quick to embrace the technology. The gastroenterology community has begun to make use of it, however.
“For some reason, in GI, PCR testing is being reimbursed better,” he said. “In our practice, we are utilizing the GI panels a lot, because we have a lot of children with diarrhea, and we can get results back in 12 to 24 hours, which can really change the course of their illness. We can stop something that would have been a three-week diarrheal course and change it to a three or four-day course. Diarrhea is still the biggest killer in the world, so PCR technology is a big deal. It’s terrific for GI. We’ve seen success in GI, and I think there could be success in the urine world.”
It’s a balance of accuracy vs. time. “If you are looking for one thing specifically — one virus, one cause of a urinary tract infection – PCR is always going to be accurate,” Carter said. “But if you are looking for a broad possibility of infections, PCR is difficult because you can only test one at a time. Culture is always going to be more accurate, because it will catch everything, but PCR, in certain infections, hopes to be as accurate with a much faster speed. PCR testing will never become more accurate than culture. That’s not its goal and purpose. Its purpose is speed.
“In a mild urinary tract infection, without fever, there’s probably no benefit to PCR. In terms of rescuing lives, PCR really matters with pyelonephritis.”
Carter predicts advances in the future that will make PCR testing even more effective. “I hope that one day not too far in the future, you don’t have to specify what you are looking for,” he said. “You can run a test that actually identifies DNA without needing to type it in. Right now it only looks for what you designate it to look for. There could come a day when you put in a substance and it tells you what DNA is present, without you having to type in the parameters. I think by the time the self-driving car is around, the self-driving test will be too.”
In the meantime, Carter is keeping an eye on advancements in PCR tests and using it when financially feasible for his patients. “We are waiting for more uniform coverage before we offer it for UTIs.”