Automated urinalysis and urine culture testing are frequently used in the emergency department (ED) setting to detect urinary tract infections. The frequent use of these tests, however, often results in a large proportion of negative cultures. The yield for urine culture is low not only when utilized in a population with undifferentiated abdominal pain, but also among uncomplicated patients with typical urinary tract infection (UTI) symptoms 1, 2, 3, 4. More selective use of urine culture testing may improve resource stewardship and reduce costs. These costs impact both EDs and clinical laboratories, including the time and resources used to collect samples for culture, laboratory culture supplies, the time and effort required to process large numbers of negative cultures, and resources devoted to the follow-up of ED culture results.
Reflex urine culture cancellation offers one possible solution to the problem of excess urine culture utilization. Reflex laboratory testing involves using information from a preliminary test to make automatic or reflexive decisions about the need for additional testing. For example, when testing for streptococcal pharyngitis, some experts recommend performing a confirmatory throat culture reflexively if an initial rapid antigen test is negative (5). This concept can be applied to urine culture utilization by implementing a laboratory protocol under which orders for urine cultures are canceled if an accompanying automated urinalysis does not meet prespecified criteria.
Urinalysis reflex testing has been previously investigated in a population of male urology clinic patients (6). It has also been recommended as a way to limit wasteful testing based on an analysis of a small group of patients in a Family Practice outpatient clinic (7). However, these algorithms have not been investigated in an ED setting. The goal of this study was to develop an easily implemented and widely applicable reflex culture cancellation protocol based on automated urinalysis results that could be used to limit urine culture utilization in samples unlikely to grow pathogenic organisms.
This was a retrospective study of patients presenting to the ED during a 6-month period between July 1, 2009 and January 1, 2010. Our Institutional Review Board approved this investigation and waived the requirement for written informed consent.
This study was performed at the University of North Carolina Medical Center (UNC), a suburban, tertiary-care academic medical center in the Southeastern United States with an annual ED census of approximately 65,000 patients per year. This ED serves a
During the 6-month study period, there were 1607 paired urinalysis and urine culture samples collected. After removing duplicate cultures performed on the same day, a total of 1546 ED patients aged 5 years and older had both a urinalysis and a urine culture ordered during their ED visit, thereby meeting inclusion criteria. The majority of included patients were female (72%) and white (53%), with a median age of 39 years (interquartile range = 31 years, range 5–101 years). Twenty-nine percent of
Urine culture testing frequently results in no organism growth, or the growth of clinically insignificant organisms 1, 2. The results presented here suggest that a reflex urine culture cancellation protocol in the ED may reduce the use of unnecessary cultures while identifying a large majority of pathogenic organisms. The potential elimination of 39% of urine cultures ordered in the ED represents a substantial savings in the clinical and laboratory resources required to collect, process, and
In conclusion, the implementation of a reflex urine culture cancellation protocol may reduce the number of unnecessary urine cultures performed in the ED, while maintaining an acceptable false-negative rate. Prospective validation is necessary to confirm these results.
1. Why is this topic important? Urine culture testing is commonly ordered in the emergency department (ED). Collecting and performing a urine culture utilizes both ED and laboratory resources, though failure to yield bacterial growth is common. This studyArticle Summary
2. What does this study attempt to show?
We wish to acknowledge Dr. Fran Shofer for her assistance with study design and statistical analysis. No external funding was obtained. Dr. Culbreath is currently employed by Tricore Reference Laboratories, an independent not-for-profit clinical laboratory.
Notably, the PPVs of UA in these two studies were only 47% and 39%, respectively [27,28], clearly indicating that a positive UA alone is not a good predictor for UTI but rather should be used to help rule out UTI by assessing for inflammation in the urinary tract in the setting of UTI symptoms. High rates of ASB present in the population combined with the low PPV of UA screening also highlight the importance of restricting RUC to patients with high clinical suspicion for UTI [19,27,28]. Though FN rates in the range indicated in the studies above (3.5 to 7%) may be acceptable “miss” rates for some patient populations, they may be unacceptable for populations where even ASB poses a high risk, such as pregnancy or immunocompromised patients, and in the setting of urogenital procedures [27,29].
Although there is evidence for a high negative predictive value for the reflexive criteria that were used in this study, one study limitation was that there is currently no gold standard regarding the degree of pyuria or other U/A criteria that should be used to trigger a reflexive culture. Previous studies have noted that the absence of pyuria, leukocyte esterase, and nitrite on a U/A is a strong predictor of a negative urine culture.8,12-14 A study including 874 men noted that the absence of pyuria (defined as <5 WBC/HPF) had a negative predictive value (NPV) of 97% for a positive urine culture.12
Reprints are not available from the study authors.
