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  Cloudy or clear? Best forecasts for urine cultures

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November 2006

Feature Story

Ed Finkel

Refrigeration, explanation, and centralized specimen processing seem to make the difference when it comes to urine culture contamination rates, according to a CAP Q-Probes study.

"This is one of the few tests where the patient, himself or herself, collects the specimen. If the patient doesn’t do it properly, there is a very high chance the specimen is contaminated," says Leonas G. Bekeris, MD, chair of the Department of Pathology at Phoenixville (Pa.) Hospital.

Suspect results can lead to additional cultures or procedures, and patients "may get antibiotics they don’t need," says Dr. Bekeris, who is co-author of the study with Bruce A. Jones, MD, senior staff pathologist at Henry Ford Hospital, Detroit, and Paul N. Valenstein, MD, president of Pathology and Laboratory Management Associates, Ann Arbor, Mich., and chair of the CAP Quality Practices Committee, of which Drs. Bekeris and Jones are members.

Of 14,739 urine culture samples from 127 institutions, almost 18 percent were contaminated, classified as such if the culture yielded at least 10,000 colony-forming units of two or more different organisms. "The study used a fairly basic, concise definition...that pretty much everybody could agree with," Dr. Jones says.

The median institution had a contamination rate of 15 percent, while the range spanned from 0.8 percent to 41 percent. "The question is, why is there so much variation?" Dr. Jones says. "It’s a good-news, bad-news [scenario]. The good news is, there are significant numbers of laboratories with low contamination rates, which means there is potential for improvement [for the rest].

"To say, ’We had a 40 percent rate, that’s as good as can be done, we have to live with it,’ should not be the reaction," he adds. "Rather, such labs should think: Other people have figured it out. We have to be a little more introspective, and study our processes, and try to identify what can be done to improve this."

The concern, in looking at the study’s data, Dr. Jones says, is the realization that in many institutions there is a substantial rate of contamination. That means the "information needed for taking care of the patient is either not going to be available or will be clouded and may result in unnecessary repeat testing or unnecessary treatment."

The study found that laboratories themselves typically have a stricter measure of what constitutes a contaminated sample than was used in the study. By their own measurements, about 10 percent of the laboratories had at least 50 percent contamination rates, significantly higher than the 41 percent peak reading using the study definition.

"Their own criteria result in a higher percentage of contamination than the study did, which means that for the actual, real-world application for patients, [contamination rates are] even higher," Dr. Jones says.

The study suggests several ways in which these rates could be lowered. For one thing, the authors examined whether patient education made a difference in whether samples were collected properly. Most of the study’s participants provided collection instructions, and 88 percent provided kits with cleansing pads, antiseptic solutions, or both.

Noteworthy differences emerged, however, in how instructions were delivered—and to whom. An oral explanation of how to collect the specimen lowered the contamination rate for male but not female patients, with a contamination rate of four percent at the 53 institutions where more than 75 percent of males were given oral instructions. At the 26 institutions that did not provide oral instructions, the contamination rate was 10.5 percent.

The study found a significant difference between samples from males (9.2 percent of which were contaminated) and females (20.8 percent of which were contaminated). At the median institution, those rates were 7.4 percent and 17.3 percent, respectively. Dr. Jones says the discrepancies between male and female patients have been well established in other studies and were not a surprise.

"Most everyone has instructions and, to some degree, provides instructions," he says. "But there may be a component of how you go about doing this that may influence the outcome and the rate of contamination. That requires more investigation, to find out what about the instruction step actually has an impact. Is it how it’s written? Is it providing written versus verbal [instructions]? If it’s verbal, what is the content of the verbal?" Though firm answers to such questions haven’t been identified, Dr. Jones notes, this is one area where labs with high contamination rates should focus their attention.

In the Q-Probes study, oral explanations did make a statistical difference for males but not for females. Dr. Bekeris has a hunch why: "The study was not designed [to measure] this, but I wonder about the quality of the [oral] instructions patients are getting. Maybe people are reticent to do a very detailed description for a female patient on how to collect a specimen. Maybe there is a social factor there."

This could be especially true if female patients are getting instructions across a counter in an open public area, for example. "Maybe somebody is just telling the patient, ’Go and read what is on the wall,’" he says. "The patient does not read it or does not understand it. This is something I think should be investigated further."

One way to address this possibility and otherwise strengthen patient education would be to provide regular training for employees. The study showed that most laboratories train physicians and phlebotomists only when they’re hired or when necessary, Dr. Bekeris says. Laboratories need to examine "the number of times somebody provides instruction to the person in the laboratory on teaching the patient how to collect the specimen." Only 13 percent of laboratories retrain their personnel annually in how to collect urine specimens for culture, according to the study.

Written instructions in the emergency department lowered the rate for men and women. At the 56 institutions where more than 75 percent of patients received those instructions, the contamination rate in specimens was 13.4 percent, as compared with a 23.3 percent rate where written instructions were not offered.

The study found the use of centralized specimen processing areas in the laboratory reduced the contamination rate for males: 4.6 percent of male samples were contaminated at the 46 institutions that had a central processing area, compared with 8.6 percent at the 45 that did not. "If they had a centralized specimen processing area, their contamination rates were lower because that area has a better handle on how to process the specimen, and they’re more standardized," Dr. Bekeris says.

Another notable finding: Refrigeration of samples reduced the contamination rate for all samples, with a rate of only 8.3 percent at the 51 institutions that reported using refrigeration, compared with 16.3 percent at the 52 that did not and instead relied on a preservative to ensure the samples’ integrity.

"What we notice is, the way the specimen is handled seems to make a difference. At room temperature, bacteria will grow and multiply," Dr. Bekeris says. "Some of the bacteria found in urine have very fast replication times; in 20 minutes, they will double the number of bacteria that are present. When you refrigerate the specimen, it makes a difference."

"One, if not the primary, association with better performance, which means lower contamination rates, was building refrigeration into the specimen handling processing steps," Dr. Jones confirms. "Those that more routinely refrigerated specimens reduced their contamination rates, which I think is a good piece of information for laboratories to be aware of and look at—where in their process they can appropriately institute that step. That is likely to help bring their rates down."

The study also found that labs that pre-screen the samples reported higher contamination rates, with 20.3 percent of pre-screened samples being contaminated, compared with 16.3 percent of those not pre-screened. Twenty-five percent of participating laboratories pre-screen their samples.

Differences showed up based on age, too, with the samples of participants under age two (5.3 percent) much less contaminated than the specimens of those between ages two and 50 (20 percent) and older than 50 (16 percent). Where samples were collected mattered little, whether in the emergency department (18 percent), site adjacent to the lab (18.7 percent), or site not adjacent to the lab (17.3 percent).

Opportunities for improvement are plentiful—"mostly [through] personnel training and how [laboratories] handle the specimen...after it is collected, and the way they process the specimen," Dr. Bekeris says. "Prompt and proper handling are important...Only a few laboratories are retraining their personnel on how to give the instructions. That’s something laboratories need to focus on."

Even simple changes in routine can make a difference, Dr. Bekeris says, recalling the experience of another member of the CAP Quality Practices Committee.

"She had a problem where patients’ urine specimens, for females, were coming back contaminated. The patient was being told to read the instructions in the bathroom, but they were placed in a way that patients could not read them easily," he says. "Just moving the instructions changed [contamination] rates for the better."


Ed Finkel is a writer in Evanston, Ill. For more information about the CAP’s Q-Probes program or to enroll, call 800-323-4040 option #1.