Fewer urine cultures — series of changes add up

Amy Carpenter Aquino

November 2020—Five years after putting in place a urine reflex algorithm at Barnes-Jewish Hospital in St. Louis, and many tweaks later, Melanie Yarbrough, PhD, D(ABMM), D(ABCC), has tips to share on how to increase the odds for success in reducing the number of urine cultures. But even for Dr. Yarbrough and colleagues, use of the algorithm remains a work in progress.

“What we implemented five years ago is almost unrecognizable to what we have now because we’ve tweaked it as we’ve gone along,” says Dr. Yarbrough, assistant medical director of clinical microbiology and assistant professor, Department of Pathology and Immunology, Washington University School of Medicine.

The consolidated microbiology laboratory at Barnes-Jewish Hospital performs testing for five hospitals. “Even though we’ve taken on more and more microbiology work from these hospitals,” she says, “we’ve still seen a decrease in our urine culture rates steadily each year over the past five years as we’ve refined the algorithm.”

Dr. Yarbrough and colleagues have also seen a concurrent increase in the lab’s urine culture positivity rate. “While this could be due to a number of factors, it’s a good sign that the reflex algorithm is contributing to this increased positivity rate by eliminating some of those unnecessary urine cultures that would have been negative,” she says.

The urine reflex algorithm works by reflexing to urine culture based on preset criteria for urinalysis results, and the criteria have changed over the years. “Our current reflex algorithm reflexes off of 10 white blood cells per high-power field,” she says. “Initially, we included other parameters such as blood, protein, leukocyte esterase, and nitrites. Subsequent studies have shown that 10 white blood cells per high-power field is a good predictor that is sensitive and yet specific enough to not miss too many positive urine cultures, so we tweaked our parameters to increase specificity and further improve our utilization.”

A retrospective study of the inpatient urine culture rates before and after changes were made to commonly used order sets in the computerized physician order entry system revealed a 45 percent reduction in the number of urine cultures performed. Dr. Yarbrough and her coauthors estimated laboratory cost savings of $103,345 in inpatient urine culture testing during the post-intervention period of May 2016 to August 2017 (Munigala S, et al. Infect Control Hosp Epidemiol. 2019;40[3]:281–286).

The catheter-associated urinary tract infection rate remained unchanged after the intervention, says coauthor David Warren, MD, MPH, professor of medicine, Division of Infectious Diseases, Washington University School of Medicine. “There was no change, which suggested that we weren’t missing catheter-associated infections. That was a positive.”

“You can conversely look at it as some of those CAUTIs may meet the [National Health Care Safety Network] definition because of the way the definition is structured. If you have a fever due to any cause, you have a CAUTI with a positive urine culture and a catheter in place, so there is probably a lot of misclassification.” Theoretically, then, the CAUTI rate will decline, he says, because those patients are not being tested unnecessarily.

“Our first big lesson was to standardize specimen collection,” Dr. Yarbrough says. “We had good success when we switched to a prepackaged urine collection kit.” It contained a collection cup and two vacutainer tubes: one tube for urinalysis and the other with boric acid preservative for culture.

“Having both of these tubes is a requirement for the reflex order because it allows us to extend the stability of the specimen for culture and permits add-on testing if a physician still wants the culture, even though it is first cancelled under the algorithm,” she explains.

The ability to add on a urine culture test for up to 48 hours alleviated a worry of the ordering physicians, Dr. Warren says, “that if they didn’t order the urine culture now, then the patient might receive antibiotics and that may somehow impact the results. So they tended to order urine cultures at the same time they were ordering urinalysis. This helped reassure them that that option was still available if they wanted it.”

Dr. Yarbrough advises laboratories that may move to adopt a urine reflex algorithm to consider workflow and storage requirements for maintaining extra urine specimens for up to 48 hours. “Having this collection kit will likely increase the number of tubes handled by the laboratory, so one thing the lab needs to do is to decide on an efficient workflow. Who is going to handle the tubes, and what part of the laboratory will ensure that reflex cultures get ordered and processed appropriately according to the urinalysis results?”

The core laboratory at Barnes-Jewish Hospital was designated to handle the lion’s share of the urine specimen management because the microbiology laboratory was not set up to receive so many additional urine specimens daily. However, the core laboratory was not accustomed to saving urine specimens for the 48 hours required for the urine reflex algorithm. “They were tossing them within 24 hours,” Dr. Yarbrough says.

The microbiology and core laboratories collaborated to design a urine specimen storage solution that would accommodate the extra tubes. “It needed to be streamlined and efficient so that it wasn’t a lot of extra work, yet organized in a way where the urine specimen could be quickly found if a urine culture needed to be added on,” Dr. Yarbrough says. The result was a rack system with tracking using a specimen management software, “so the urine specimen’s location was always known.”

Test names should be clear, she says, and they should not contain lab lingo that providers do not understand. “That was one of the things we tweaked almost as soon as we introduced the reflex order. We quickly realized that physicians didn’t understand what we were talking about because we had used some lab lingo in our test orderable names.”

Dr. Warren agrees: “Naming conventions matter. Before, we had what we called a ‘urine flex’ and ‘urine reflex,’ and to this day I can’t remember which one was which.”

Making the urine test names more self-explanatory was one of the most significant changes made to the CPOE system, he says. “We changed them to ‘urinalysis with reflex to microscopy’ or ‘urinalysis with reflex to microscopy and culture.’ It was much more straightforward naming, and that is very important for physicians on the floor because they may not think of these tests in the same way as the laboratory would.”

In another refinement, the team worked with Epic to add an entry requirement for the urine specimen source. “Specimen type matters for urine culture because often hospitals have different thresholds for a positive urine culture depending on the specimen type,” Dr. Yarbrough says. To help with its interpretation of urine culture results, the laboratory created a prepopulated list of specimen types—in-and-out catheter, indwelling catheter, suprapubic aspirate, suprapubic catheter, and clean-catch specimen.