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Indian Pediatr 2011;48:
816-817 |
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Gram Stain as a Predictor of Urinary
Infections in Children under 2 years |
MJ Rodríguez, A Rodríguez and R Marañón
Pediatric Emergency Section, HGU Gregorio Marañón,
Madrid, Spain.
Email: [email protected]
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During early life, clinical manifestations of urinary tract infection (UTI)
are nonspecific and definitive diagnosis through urine culture is often
late. It is essential to have rapid and reliable diagnostic tests to guide
initial treatment. We compared the diagnostic effectiveness of the urine
dipstick, urine sediment, and Gram stain in infants with suspected UTI.
This was a retrospective study conducted by reviewing
medical records of patients admitted to the pediatric emergency service
during the past five years. We included patients aged up to 24 months with
symptoms suggestive of UTI, in which a urine sample was obtained by
bladder catheterization to perform urine dipstick, urine sediment, gram
stain and urine culture. The presence of leukocyte esterase and nitrites
of 1+ or greater by dipstick were considered positive. Leukocyturia was
defined as >10 leukocytes per high power field in centrifuged urine; and
bacteriuria as the microscopic visualization of any number of bacteria.
Gram stain positivity was defined as the isolation of more than 1 bacteria
per high power field of any organism in centrifuged fresh urine. The
results of these tests were compared with the urine culture as gold
standard (positive if >10,000 cfu/mL of a single pathogen). We determined
the sensitivity, specificity, positive and negative predictive value, for
each of the parameters analyzed. We also compared the results of Gram
stain by stratifying patients according to age group (£3
months and >3 months).
During the 5-year study period, 980 patients met
inclusion criteria; 430 were girls and mean age was 6 months. Urine
culture was positive in 558 cases. Urine dipstick showed leukocyte
esterase to be the most sensitive parameter, although nitrites were the
most specific (Table I). Similar values were found for the
presence of leukocytes and bacteria in the urinary sediment. Gram stain
showed the highest diagnostic effectiveness. There were no differences of
the value of gram stain in those below and above 3 months of age.
TABLE I Utility of Screening Tests for Diagnosis of Urinary Tract Infection
|
S (%) |
Sp (%) |
PPV (%) |
NPV (%) |
Urine dipstick |
Leukocyte esterase |
76 |
84 |
86 |
73 |
Nitrites |
31 |
99 |
97 |
53 |
Leukocyte esterase and Nitritess |
26 |
99 |
42 |
51 |
Normal |
80 |
83 |
86 |
77 |
Urine sediment |
Leukocyturia |
75 |
84 |
86 |
72 |
Bacteriuria |
42 |
71 |
94 |
56 |
Leukocyturia and bacteriuria |
38 |
98 |
96 |
55 |
Normal |
79 |
83 |
85 |
75 |
Gram
stain |
83 |
97 |
97 |
82 |
S: sensitivity; Sp: Specificity; PPV: Positive predictive value; NPV:
Negative predictive value. |
Screening tests are essential to guide diagnosis and
initial treatment of UTI in children until the results of urine cultures
become available [1,2]. Urine dipstick has been reported to have lower
sensitivity in incontinent children, as decreased nitrite production and a
less intense inflammatory response due to more frequent urination [3].
This is confirmed in our series. While urine dipstick is a fast and
affordable method for initial diagnosis in the emergency department [4],
its sensitivity was 80%. Similarly the diagnostic utility of urine
sediment was also limited. In contrast, gram stain provided a higher
sensitivity and specificity applicable not only to children under 3 months
but extendable to 24 months, and was thus a reliable guide for initial
antibiotic treatment [5].
Our results show that gram stain was the diagnostic
tests of choice for decision making in infants with suspected UTI until
the results of urine culture are available.
References
1. Bauer R, Kogan BA. New developments in the diagnosis
and management of pediatric UTIs. Urol Clin North Am. 2008;35:47-58.
2. Chang SL, Shortliffe LD. Pediatric urinary tract
infections. Pediatr Clin North Am. 2006;53:379-400.
3. Waisman Y, Zerem E, Amir L, Mimouni M. The validity
of the uriscreen test for early detection of urinary tract infection in
children. Pediatrics. 1999;104:e41.
4. Ochoa Sangrador C, Conde Redondo F. Utility of
distinct urinalysis parameters in the diagnosis of urinary tract
infections. Ann Pediatr (Barc). 2007;67:450-60.
5. Williams GJ, Macaskill P, Chan SF, Turner RM, Hodson
E, Craig JC. Absolute and relative accuracy of rapid urine tests for
urinary tract infection in children: a meta-analysis. Lancet Infect Dis.
2010;10:240-50.
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