Urine cultures are the most frequently ordered microbiologic test, with the majority of specimens submitted from asymptomatic patients. Urine cultures should only be ordered if patients have symptoms localizing to the urinary tract such as acute dysuria, urgency, frequency, suprapubic or flank pain or fever without an obvious alternate source. Outside of these specific symptoms, positive cultures indicate asymptomatic bacteriuria and frequently result in antimicrobial therapy that is of no benefit and is potentially harmful. Cloudy or malodorous urine are not specific findings of urinary tract infection and should not prompt culture unless acute urinary tract symptoms are present. Delirium is not considered a symptom of cystitis in non-catheterized patients. In catheterized patients with fever or delirium, a positive urine culture may still represent asymptomatic bacteriuria unless alternate sources have been excluded. Laboratories should consider supplementing educational efforts to reduce collection of urine cultures from asymptomatic patients with analytical interventions that reduce processing of low-value specimens.
Hartley S, et al. Inappropriate testing for urinary tract infection in hospitalized patients: an opportunity for improvement. Infect Control Hosp Epidemiol. 2013 Nov;34(11):1204-7. PMID: 24113606.
Leis JA, et al. Reducing antimicrobial therapy for asymptomatic bacteriuria among noncatheterized inpatients: a proof-of-concept study. Clin Infect Dis. 2014 Apr;58(7):980-3. PMID: 24577290.
McKenzie R, et al. Bacteriuria in individuals who become delirious. Am J Med. 2014 Apr;127(4):255-7. PMID: 24439075.
Nicolle LE, et al. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005 Mar 1;40(5):643-54. PMID: 15714408.
Related Resources:Share on Facebook Share on Twitter
Only liquid stool specimens should be collected or processed for C. difficile detection, as a positive test in the absence of diarrhea likely represents C. difficile colonization. Diagnostic gains are minimal with repeat C. difficile nucleic acid amplification testing within 7 days of a negative test. Repeat C. difficile toxin testing by enzyme immunoassay within 7 days of a prior negative test is also of little incremental diagnostic yield but may be warranted in select cases. Test of cure in patients with recent C. difficile infection is also not recommended. Prior investigations have shown that the use of hospital information systems to restrict ordering of repeat tests for these reasons resulted in a 91% reduction in repeat testing.
Aichinger E, et al. Nonutility of repeat laboratory testing for detection of Clostridium difficile by use of PCR or enzyme immunoassay. J Clin Microbiol. 2008 Nov;46(11):3795-7. PMID: 18784320.
Luo RF, et al. Is repeat PCR needed for diagnosis of Clostridium difficile infection? J Clin Microbiol. 2010 Oct;48(10):3738-41. PMID: 20686078.
Luo RF, et al. Alerting physicians during electronic order entry effectively reduces unnecessary repeat PCR testing for Clostridium difficile. J Clin Microbiol. 2013 Nov;51(11):3872-4. PMID: 23985918.Share on Facebook Share on Twitter
All wounds are colonized with microorganisms. Cultures should not be obtained from wounds that are not clinically infected (i.e., absence of classical signs of inflammation or purulence or increasing pain). For wounds that are clinically infected, the ideal specimens for culture are deep specimens that are obtained through biopsy or deep curettage following cleansing/debridement of the wound. Laboratories should consider use of screening criteria to reject such swabs without proceeding to culture. For superficial swab specimens that are processed/cultured, interpretation of the results should be correlated with the Gram stain.
Chakraborti C, et al. Sensitivity of superficial cultures in lower extremity wounds. J Hosp Med. 2010 Sep;5(7):415-20. PMID: 20845440.
Gardner SE, et al. Cultures of diabetic foot ulcers without clinical signs of infection do not predict outcomes. Diabetes Care. 2014 Oct;37(10):2693-701. PMID: 25011945.
Lipsky BA, et al. 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clin Infect Dis. 2012 Jun;54(12):e132-73. PMID: 22619242.
Matkoski C, et al. Evaluation of the Q score and Q234 systems for cost-effective and clinically relevant interpretation of wound cultures. J Clin Microbiol. 2006 May;44(5):1869-72. PMID: 16672426.Share on Facebook Share on Twitter
Although nucleic acid amplification testing is the modality of choice for determining the viral etiology of meningitis/encephalitis, it should not be requested routinely on all cerebrospinal fluid specimens. The routine use of these tests in patients without compatible clinical syndromes can result in unnecessary empiric antiviral treatment, additional care, and prolonged length of hospitalization for patients awaiting testing results. Additionally, routine testing may result in depletion of cerebrospinal fluid needed for other diagnostic purposes. In cases where nucleic acid testing is requested for adults, laboratories should have policies for when testing will be performed if the cerebrospinal fluid cell count and protein are normal.
Hanson KE, et al. Validation of laboratory screening criteria for herpes simplex virus testing of cerebrospinal fluid. J Clin Microbiol. 2007 Mar;45(3):721-4. PMID: 17202281.
López Roa P, et al. PCR for detection of herpes simplex virus in cerebrospinal fluid: alternative acceptance criteria for diagnostic workup. J Clin Microbiol. 2013 Sep;51(9):2880-3. PMID: 23804382.
Saraya AW, et al. Normocellular CSF in herpes simplex encephalitis. BMC Res Notes. 2016 Feb 15;9:95. PMID: 26879928.Share on Facebook Share on Twitter
Fluids and tissue specimens can usually be obtained in the controlled setting of the operating room and represent higher quality specimens than swabs. Culture of swab specimens is associated with increased false negative results, as they are inferior in recovering anaerobic bacteria, mycobacteria and fungi, and provide inadequate volumes to perform all necessary diagnostic tests. To encourage collection of fluid and/or tissue samples, consideration should be given to making swabs unavailable in the operating room without specific request.
Baron EJ, et al. A guide to utilization of the microbiology laboratory for diagnosis of infectious diseases: 2013 recommendations by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). Clin Infect Dis. 2013 Aug;57(4):e22-e121. PMID: 23845951.
Koneman EW. Koneman’s Color Atlas and Textbook of Diagnostic Microbiology. Lippincott Williams & Wilkins, 2006.Share on Facebook Share on Twitter