Lab Rounds: Diagnosis of Pediatric UTI’s

Chris McCrossin

Outline• To Review methods of urine collection

• Sensitivity, specificity, and clinical use of:– Urinalysis– Microscopy– Culture

Case 1: Methods of Collection

• 18 m/o F presents with one day history of fever and one episode of vomiting; otherwise well looking child

• No clear focus of infection you want to rule out UTI

• How do you collect the urine?

Collection Options• Infants and Non-toilet trained children

• Possibilities for collection– Catheter specimen– Suprapubic (gold standard)– Bagged specimen– Clean catch

Bag Specimen vs Clean Catch

• Best evidence topic report in EMJ 2006

• Authors found two relevant papers between 1966 and 2005

• Disclaimer: The following discussion is to look at the use of bag specimens and dip to screen who needs to be catheterized. Bagged specimens should never be sent for culture

Bag Specimen vs Clean Catch

• Alam et al 2005

• 191 children <3 yrs of age (125 were boys)

• All had attempts at clean catch and urine bag sampling

• Looked at bacterial contamination:» 14.7% contamination with clean catch» 26.6% contamination with bag specimen

Bag Specimen vs Clean Catch

• Hardy et al 1976• 30 unwell children with suspected UTI• Compared clean catch with bag and

suprapubic aspiration of urine• Results:

» Bag specimens 4/30 pure growth, 22/30 contaminated

» Clean catch 2/30 pure growth, 22/30 contaminated

Bag Specimen vs Clean Catch

• According to their “best evidence” review there is one paper (with significant weaknesses) that suggests clean-catch is a better non-invasive technique when compared with bag specimens

Bag vs Catheter• McGillivray et al 2005 compared the use

of bag versus catheter urinalysis in children under 3 “at risk for UTI”

• Results:• Urine Dip

» Bag 85% sensitive, 62% specific» Cath 71% sensitive, 97% specific» Neonates <90 days old had sensitivity of 69% for

bag, 46% for cath

Bag vs Cath• Authors conclude that although small

sample size of infants, the low sensitivity of dip regardless of collection technique requires the culture of a catheter specimen in the under 90 day old age group

• Dipstick will miss 4-12% of UTI’s in this age group

Bag vs Cath• Authors also suggest:

• “children with fever without source at low risk for UTI (no previous history of UTI, no anatomic abnormalities, not immunosuppressed, no urinary symptoms), a selective cath strategy as outlined in the AAP practice parameter appears reasonable”

• A reduction of catheterizations of 46% in non-toilet trained peds older than 90 days (reduction potentially even greater in a population with lower rate of UTI’s than in their study population

Questions for you

• Is it practical in a busy emerg to use bags or clean catch urines for screening who needs catheterization?

• Are we able to accurately assess who is at “low risk” for UTI in emerg?

In and Out Cath• Cons:

• Invasive• May need to do it several times to get urine• Chance of introducing infection• Chance of urethral trauma

• Pros• Next best method after suprapubic cath in

terms of avoiding a contaminated specimen

Use of Ultrasound in Urethral Catheterization

• Lei et al 2005 published in Pediatrics

• Prospective study using bedside U/S pre-cath to determine urine bladder volume in ages 0-24 months

• Methods:» 2 phases» 1st phase: immediate cath in 136 patients» 2nd phase: initial scanning in 112 patients prior to cath

Use of Ultrasound in Urethral Catheterization

• Results:– Initial phase: 72% success rate with initial catheterization– Intervention phase:

» Sufficient urine identified in 76% with a success of first cath in 98% of those patients

» Patients without sufficient urine were rescanned every 1/2 hour with all showing enough urine within 90 minutes. 93% underwent initial successful catheterization

» Overall successful first cath in intervention phase was 96%

• Authors conclude able to avoid repeated cath with a safe non invasive procedure

AAP Recommendations• Aspiration or urethral catheterization to

establish a diagnosis of UTI in neonates and young children if antibiotics required

• In an infant or child 2 months to 2 years of age with unexplained fever not so ill as to require immediate antimicrobial therapy there are two options:

– Obtain culture by SPA or cath– Perform urinalysis by most convenient means. If

suggestive of UTI then do a cath/SPA. If cath urinalysis - then watch over time

Next Case:• So now you have a 4 month old F

patient who is febrile, no specific UTI risk factors, and normal R&M

• Do you send for culture?

• Would it make a difference if she was 3 years old and had burning with urination?

Urine Dip in Pediatric Population

• Overall has a sensitivity of 80%

• Prevalence of UTI is estimated at 5%

• Rate of UTI in a negative urinalysis is expected to be about 1.3%

» Newman, Takayama: Urinary tract controversy and questions (letter). Pediatrics 101:731-732

Urine Dip Components: Leukocyte esterase

• Positive results from presence of significant leukocytes in the urine

• Anything that gives pyuria can result in a positive test

• A negative test result coupled with a lack of urinary symptoms is usually sufficient to rule out UTI

» Liao et al 2001 Ped Clinics NA

Urine Dip Components: Nitrites

• Gram-negative rods (ie E Coli) contain the enzyme nitrate reductase (NR)

• This enzyme converts dietary nitrate in the urine to nitrite

• Causes of False Negatives:» Inadequate dietary nitrate» Bacteria lacking NR» Urine samples not incubated for long enough in the

bladder

• First morning samples are most sensitive

…but keep in mind:• Consequence of missing a UTI is

significant in both the short and long term

– Urosepsis– Missed urinary tract abnormality– Renal scarring leading to HTN, ESRD

» Santen, Altieri. Pediatric Urinary Tract Infection. Emerg Med Clin N A. 2001: 19(3)

Potential Guidelines for sending cultures with negative Dip/Microscopy

• Send culture anyway for all febrile infants under 2 years of age

• Children with history of previous UTI

• Children on antibiotic therapy

• In children whom empiric therapy is started

Clinical pearl• Girls less than 2 years and boys less

than 6 months with fever and a probable source of fever (otitis media, URI) have a significant rate of UTI being about 5%

Case 3• 3 month old F with fever• Initial Test Results

• Dip» No Leukocyte Esterase» No Nitrites

• Microscopy» 5-10 leuks» No erythrocytes

• Now what do we do? Treat as UTI?• What if she was 4 years old with dysuria? 4

years old and no dysuria?

Pyuria on Microscopy• >5 WBC/HPF

• Sensitivity: 54-85%• Specificity: 70-81%

• Microscopic notation of bacteria• Sensitivity: 60-90%• Specificity: 80-90%

• Results depend on• Volume of urine, observer error, force and

duration of centrifugation

Urine Dip vs Microscopy• Meta-analysis published in Pediatrics in 1999

by Gorelick and Shaw– Conclusions:

• Dipstick and gram stain perform similarly in detecting UTI in peds with high sensitivity and low FPR

• These tests have better sensitivity and specificity than the presence of pyuria in either centrifuged or uncentrifuged specimen

• TPRs and FPRs of the presence of >5 WBC/hpf in a centrifuged urine specimen is sufficiently poor that it cannot be recommended for making a presumptive diagnosis of UTI

Urine Dip vs Microscopy• Meta-analysis in 2001 by Huicho and

colleagues found conflicting results• They conclude: “pyuria >/= 10 wbc/hpf and

bacteriuria are best suited for assessing the risk of UTI in children”

• They felt that dipstick tests in the diagnosis of UTI’s in children could not be definitively assessed because number of studies addressing this specific point are small

To keep in mind…• Incidence of UTI in the 2 and under age

group is 5% and may cause few recognizable signs or symptoms other than possibly a fever

• Greater potential for renal damage compared with older children

• Meta-analysis by Huicho suggests that “enhanced urinalysis” with gram stain or hemocytometer cell count being positive is the most sensitive method for screening for UTI

Case 3• You are reviewing labs from a previous shift

and find a positive urine culture in a 3 year old girl who had a normal urinalysis and microscopy

• You call the parents and she is intermittently febrile with a cough (a cold has been running through the family)

• Do you prescribe an antibiotic?

Case 4• 3 y/o M with Fever

• Urine Dip and Microscopy are negative

• Are cultures necessary to rule out UTI?

Urine Cultures• Gold standard for diagnosing UTIs• Can get a false negative with betadine mixed

in the sample or if child is on antibiotics• Cultures can be positive with negative

urinalysis» Thought to occur when sample is taken in early

infection prior to local inflammatory response is present

» May also mean contamination

• Debate whether children without pyuria but positive cultures should be treated

Urine Cultures• Asymptomatic bacteriuria

• Wettergren et al followed 37 infants with culture proven bacteriuria over a 6 year period

• All went untreated• One developed pyelonephritis and no evidence of

decreased renal function at the end of the study

• Reasonable option:– If Child is asymptomatic then reasonable to repeat

urinalysis and culture if no antibiotics started– Treat if symptomatic

AAP Guidelines• Practice guidelines focus specifically on

the diagnosis of febrile infants and children <2 years of age

• Exclude children older than 2 years of age with first presentation of UTI from their review because:

– Less risk of renal scarring in this age group– More likely to have symptoms referable to the GU

tract

Summary of Sens and Spec of urine dip and microscopy

Test Sensitivity SpecificityLE 83 84

Nitrite 50 98LE or Nitrite 88 93

LE and Nitrite 72 96Microscopy: WBCs 73 81

Microscopy:

Bacteria81 83

Enhances UA (cell count or gram stain)

95 89

References• Zorc et al Diagnosis and Management of Pediatric Urinary Tract Infections. Clinical Microbiology Reviews.

2005;18(2):417-22.• Huicho et al Metaanalysis of urine screening for determining the risk of urinary tract infection in children.

Pediatric Infectious Disease Journal. 2002; 21(1):1-11.• Gorelick & Shaw Screening tests for urinary tract infection in children: a meta-analysis. Pediatrics. 1999;

104(5)• Herr et al Enhanced urinalysis improves identification of febrile infants ages 60 days and younger at low

risk for serious bacterial illness. Pediatrics. 2001; 108(4): 866-871.• AAP. Practice Parameter: The diagnosis, treatment, and evaluation of the initial urinary tract infection in

febrile infants and young children. 1999. www.aap.org• Chen et al Utility of bedside bladder ultrasound before urethral catheterization in young children. Pediatrics.

2005; 115(1): 108-111.• McGillivray et al A head-to-head comparison: clean-void bag versus catheter urinalysis in the diagnosis of

urinary tract infection in young children. Journal of Pediatrics. 2005. pp451-456.• Liao et al Pediatric Urine Testing. Pediatric Clinics of NA. 2001; 18(6).• Santen and Altieri. Pediatric Urinary tract infection. Emergency Medicine Clinics of NA. 2001; 19(3).• Jenner and Atzainia. Clean catch or bag specimen in UTI in non toilet trained children. Emergency

Medicine Journal. 2006; 2:219-220.• Chang & Shortliffe. Pediatric Urinary Tract Infections. Pediatric Clinics of NA. 2006; 53:379-400.• Whiting. Rapid tests and urine sampling techniques for the diagnosis of UTI in children under fie years: a

systematic review. BMC Pediatrics. 2005; 5(4).