Point-Counterpoint: Reflex Cultures Reduce Laboratory Workload and Improve Antimicrobial Stewardship in Patients Suspected of Having Urinary Tract Infections

Abstract

POINT How often misused tests generate misleading thoughts:an argument for the appropriate use of the urinalysis to rule out urinary tract infections.-Adapted from Herbert Spencer O ptimum use of laboratory testing requires that providers order tests only for patients with an appropriate indication; urine cultures are no exception to this rule. Guidelines published by the Infectious Diseases Society of American support urine testing and sterilization in the absence of symptoms for only two groups: pregnant women and those about to undergo urologic surgery (1). For the remainder of patients, such testing should be done only in the context of symptoms consistent with a urinary tract infection (UTI): fever, urgency, frequency, dysuria, suprapubic tenderness, altered mental status, or hypotension. And yet, up to half of patients for whom a urine test is ordered in the emergency department (ED) or general medicine services (2) do not have symptoms consistent with a UTI. Unfortunately, several studies have demonstrated that these test results, and not the patient's symptoms, drive antibiotic utilization (2-4). Such overuse of testing is problematic on several fronts, including potential misdiagnosis (i.e., early case closing and failure to evaluate for other causes of symptoms by the physician), overuse of antimicrobials and their associated risks, and a high burden of testing for the laboratory. A rapid diagnostic strategy to diagnose UTI is therefore desirable but does not exist at present. However, UA (performed either with a dipstick or an automated instrument) is thought by many to be a useful screen by which to rule out UTI in a symptomatic patient. I will demonstrate that the detection of pyuria or bacteria by UA is a screening test that, when used appropriately, is associated with a high negative predictive value (NPV) that should impart confidence to the physician that a urine culture will not yield additional, clinically relevant information (i.e., the culture will be negative), and that a UTI is unlikely to be the cause of their patient's symptoms. However, it should be emphasized that the appropriate use of UA to rule out UTI is in the context of a patient with symptoms consistent with a UTI.The absence of pyuria upon UA is an excellent predictor of a negative urine culture. One of the challenges associated with implementing a UA reflex-to-culture algorithm is the absence of evidence-based guidance on which UA parameters best predict urine culture results. Several studies have evaluated the predictive values of both indirect markers of infection: a positive result for nitrite (a marker for the presence of Enterobacteriaceae in the urine) or leukocyte esterase (LE; a marker for the presence of leukocytes) or direct observation of white blood cells (i.e., pyuria) or bacteria in the urine by microscopy. When evaluated in a population with a low prevalence of positive bacterial cultures, such as outpatients suspected of having a UTI, the NPV of any of these factors individually is excellent. For instance, a la...

Catheter-Associated Urinary Tract Infections in Adults: Diagnosis, Treatment, and Prevention

“…However, the use of reflex urine cultures remains an area of debate. 37 In addition, the Infectious Diseases Society of America recommends against screening for or treating ASB in patients with either short-term (<30 days) or long-term indwelling urethral catheters. 21 Ideally, a urine culture should be obtained by collecting a midstream sample.…”

Performance of urinalysis tests and their ability in predicting results of urine cultures: a comparison between automated test strip analyser and flow cytometry in various subpopulations and types of samples

“…For example, the NPV of 99.1% when bacterial and leucocyte counts were below the threshold in our study, meaning that only 9 out of 1000 samples will become culture positive while only around 40% of samples received need to be cultured. Screening and avoiding urine samples that will be culture negative will reduce workload and costs in routine medical microbiology laboratories 4. To the best of our knowledge, this is the first study that investigated the automated test strip analyser to rule out urine samples to be cultured.…”

“…Positive nitrite test result confirms UTI and one can initiate the treatment, and negative bacteria count excludes the possibility of UTI and treatment can be avoided. For routine laboratories, urinalysis can be used for ‘reflex urine culture’ practice, that is, avoiding the culture of urine samples in which urinalysis show high NPVs in order to reduce costs and workloads 4. For this ‘reflex urine culture’ purpose, flow cytometer showed better performance than automated test strips analyser.…”

“…In the last few years, there is a renewed interest in the use of urinalysis in a specific population such as paediatric patients2 3 9–11 and in predicting urine samples that will turn to be negative 4. Studies on test strip analyser were often performed manually 12.…”

Diagnosis of urinary tract infections: need for a reflective rather than reflexive approach

“…Although a negative urinalysis may have a high negative predictive value for bacteriuria and infection, an "abnormal" result does not indicate infection. 5 An assessment of the pretest probability (ie, symptoms and signs) is key to better identify urinary tract infection. Reflex urine cultures used in isolation enhance the identification of bacteriuria (both symptomatic and asymptomatic) but not necessarily the diagnosis of UTIs.…”