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 024 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
83
50
88
Specificity
84
98
93
72
73
96
81
Microscopy:
Bacteria
81
83
Enhances UA (cell
count or gram stain)
95
89
LE
Nitrite
LE or Nitrite
LE and Nitrite
Microscopy: WBCs
References
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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).