Urine preanalytics guideline effort highlights data need

Anne Paxton

February 2016—When it comes to recommended practices for preanalytic handling of urine specimens for the microbiology lab, Alice S. Weissfeld, PhD, D(ABMM), has a blunt and colorful take: “I call it ‘running our lab based on urban legend.’”

“The way I learned it and the way I taught it was after two hours, then either use refrigeration or boric acid, women must clean, and so on. There was no way around it.” But the foundation for those standards has been largely anecdotal experience. “The people we looked to—and they were some of the giants in the field of urine cultures—said, ‘Here is the best way to collect; here is the best way to store,’ but they basically never had any data,” says Dr. Weissfeld, president and CEO of Microbiology Specialists in Houston.

Addressing that need with an evidence-based guideline was one of the goals of a collaboration between the American Society for Microbiology and the Centers for Disease Control and Prevention whereby studies of commonly used collection, storage, and preservation methods for urine samples would be reviewed and recommendations made based on a meta-analysis of the studies.

Part of an initiative to write “Laboratory Medicine Best Practices” (LMBP) guidelines, the collaborative project used the CDC’s A-6 systematic review method to develop recommendations based on the “body of evidence.” The method is a “whole new approach” that shifts the focus from the laboratory to the patient, where it should be, to assess quality improvement practices and develop evidence-based practice guidelines, says Dr. Weissfeld, who served as an expert panel member of the Urine Collection, Preservation and Transport Working Group.

The two parameters the panel measured were reduction of urine culture contamination and increased accuracy of patient diagnosis. A January 2016 article, “Effectiveness of preanalytic practices on contamination and diagnostic accuracy of urine cultures: a Laboratory Medicine Best Practices systematic review and meta-analysis,” describes the study authors’ findings (LaRocco MT, et al. Clin Microbiol Rev. 2016;29[1]:105–147).

The results of the study reflect the relatively weak evidence to support a comprehensive guideline. Of 12 urine preanalytic practices reviewed, only three were recommended, three were not recommended, and the most frequent finding—in six cases—was “No recommendation for or against based on insufficient evidence.”

The available research does justify recommending midstream collection with cleansing for children’s urine specimens, as well as for women’s and men’s specimens, the study authors found. For women’s and men’s specimens, the authors do not recommend for or against midstream collection without cleansing. But for children’s specimens, they recommend against collection in sterile urine bags, from diapers, or midstream without cleansing. The authors also found enough strong evidence to recommend against first-void urine collection from men. As to whether urine should be stored at room temperature, refrigerated, or preserved in boric acid for delayed processing, the authors found the evidence was not strong enough to justify recommendations.

These findings don’t mean laboratories should abandon their customary practices to ensure preanalytic quality, Dr. Weissfeld stresses. And the report notes that its lack of recommendation does not preclude the use of refrigeration or chemical preservatives in clinical practice. But a key take-away message of the collaborative effort and the paper is that microbiology laboratories need to collect more data on urine preanalytics.

LMBP was one of the projects that resulted from a meeting the CDC convened several years ago. The outcome of the meeting was published in May 2008 as “Laboratory Medicine: A National Status Report,” also known as the Lewin Report. The ASM and the CDC started working together on the LMBP studies in 2011.

Nancy E. Cornish, MD, medical officer, CDC’s Division of Laboratory Systems, and scientific and technical lead on the urine preanalytics study, joined the LMBP team four years ago when she started working at the division. Six papers have been published using the CDC LMBP method of systematic review. “But since it’s still a fairly new process, we’re all learning, and improving the process, as we go.”

It’s been a while since urine has actually been studied, Dr. Cornish notes. “We’re in a new age of medicine and we have different circumstances than they did 30 years ago, so I think it’s time to re-evaluate, to see if we can build an evidence base to have us feel confident in selecting, collecting, and transporting urines.”

Urine cultures are the largest portion of many hospital-based microbiology laboratories’ workload, and some hospitals are performing hundreds of cultures a day, Dr. Cornish points out. If the specimens are poorly collected or poorly transported, culture results can be erroneous. But poor selection is just as important. “For example, if the patient doesn’t have signs and symptoms of a urinary tract infection, collecting that urine could result in growth of bacteria because patients can be colonized with bacteria periodically without infection, so you are bound to find positives.

“In the lab, we don’t know if the patient has signs or symptoms. We do our ID and our susceptibilities based on laboratory criteria for workup. The clinicians get the report with a full ID and susceptibility and may feel they need to treat the patient because the report indicates the patient may have a UTI.”

The authors looked at a series of practices, then evaluated the literature in each case to see if there was enough evidence to support a recommendation. But out of 12 questions on practices that the study authors explored, “We only could make recommendations for three of them.” Was that surprising? Yes, Dr. Cornish says. “I was trained as a clinical microbiologist and a pathologist, and I thought the guidelines I was following were based on evidence. So then to do a thorough systematic review and discover we actually didn’t have enough evidence for some of these guidelines was a surprise.”

“That doesn’t mean we are not doing the right thing,” she adds. “Maybe we are. But we don’t have the evidence to prove that.”

The CDC’s emphasis on “great data” through its systematic review process may, over the long run, help remedy the evidence gap. “To me, great data is the beauty of the CDC method,” Dr. Weissfeld says. “You start with a librarian, and it has to be a librarian trained in systematic review, and you say, OK, I need to know how many papers there are on this subject. Then you take key words and strings of words you’d like to search on—say, ‘boric acid’ and ‘preanalytic.’ And you actually look at how many articles there are and start weeding them down to ones that will answer your specific question. So everything relates back to this focused question.”

You won’t necessarily find what you expect, Dr. Weissfeld cautions. “If you can’t culture a urine specimen within two hours, does refrigeration help? We know that’s what you should do and still think that’s what we should do. But if someone were to say ‘Show me the papers,’ you can’t.”