Practice Based Learning: Urinalysis – Clean and Dirty




Presented by Alex Henri MD

How prone are UA’s to contamination, can we identify contamination on a UA, and does contamination matter?

How common is contamination?

  • “Growth of bacteria on culture without bacteria in the urinary tract.”
  • Contamination rates for clean-catch urinalysis in children vary by study: 2% – 39%

Is this contamination?

“Contamination can be identified unequivocally only by demonstrating that urine collected by suprapubic aspiration is sterile whereas a midstream urine culture grows one or more organisms.” (Stamm, 1983.)

What is the probability of true bacteriuria in symptomatic and asymptomatic patients based on +UA signs?

“Urinary tract infection: clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months.”

If a culture does grow bacteria, would we do anything about it?

In girls with ABU or “covert” bacteriuria without underlying renal abnormalities who are not treated with antimicrobial therapy, bacterial isolates tend to remain stable for several years.

Sterile pyuria

“True infection without pyuria is unusual, but pyuria can occur in the absence of apparent bacterial infection”

  • Contamination of the urine sample by the sterilizing solution used to clean the meatus
  • Contamination of the urine sample with vaginal leukocytes from vaginal secretions
  • Chronic interstitial nephritis
  • Nephrolithiasis
  • Uroepithelial tumor
  • Interstitial cystitis
  • Intra-abdominal inflammatory process adjacent to the bladder
  • Infection with atypical organisms, such as Chlamydia, Ureaplasma urealyticum, or tuberculosis


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Macfarlane PI, Houghton C, Hughes C. Pad urine collection for early childhood urinary-tract infection. Lancet. 1999 Aug 14;354(9178):571.

Subcommittee on Urinary Tract Infection, Steering Committee on Quality Improvement and Management, Roberts KB. Urinary tract infection: clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months. Pediatrics. 2011 Sep;128(3):595-610.

Kemper KJ, Avner ED. The case against screening urinalyses for asymptomatic bacteriuria in children. Am J Dis Child. 1992 Mar;146(3):343-6.

LaRocco MT, Franek J, Leibach EK, et al. Effectiveness of Preanalytic Practices on Contamination and Diagnostic Accuracy of Urine Cultures: a Laboratory Medicine Best Practices Systematic Review and Meta-analysis. Clin Microbiol Rev. 2016

Shaikh N, Morone NE, Bost JE, Farrell MH. Prevalence of urinary tract infection in childhood: a meta-analysis. Pediatr Infect Dis J. 2008 Apr;27(4):302-8.

Vaillancourt S, McGillivray D, Zhang X, Kramer MS. To clean or not to clean: effect on contamination rates in midstream urine collections in toilet-trained children. Pediatrics. 2007 Jun;119(6):e1288-93. Epub 2007 May 14.

Frazee BW, Enriquez K, Ng V, Alter H. Abnormal urinalysis results are common, regardless of specimen collection technique, in women without urinary tract infections. J Emerg Med. 2015 Jun;48(6):706-11.

Lohr JA, Donowitz LG, Dudley SM. Bacterial contamination rates in voided urine collections in girls. J Pediatr. 1989 Jan;114(1):91-3.

Savage DC, Howie G, Adler K, Wilson MI. Controlled trial of therapy in covert bacteriuria of childhood. Lancet. 1975 Feb 15;1(7903):358-61.

Lindberg U. Asymptomatic bacteriuria in school girls. V. The clinical course and response to treatment. Acta Paediatr Scand. 1975 Sep;64(5):718-24.

Cardiff-Oxford Bacteriuria Study Group. Sequelae of covert bacteriuria in schoolgirls. A four-year follow-up study. Lancet. 1978 Apr 29;1(8070):889-93.

Stamm WE. Measurement of pyuria and its relation to bacteriuria. Am J Med. 1983 Jul 28;75(1B):53-8.

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