Journal club Diagnostic accuracy of Urinalysis for UTI in Infants

Journal clubDiagnostic accuracy of Urinalysis for UTI in Infants <3 months of age

U. Majuran

16th September 2015

Structure• Current practice/ guidance

• PICO

• Paper review – Validity of study– Results– Will results change practice?

NICE guidance (2007)• “Infants and children presenting with

unexplained fever of 38°C or higher should have a urine sample within 24hrs”

Re: urine testing

• “All infants younger than 3 months with suspected UTI should be referred to paediatric specialist care and a urine sample should be sent for urgent microscopy and culture”.

(NICE)

American Academy of Pediatrics (2011)• Revised guidance• Consider urinalysis in children age 2m-2yrs alongside

culture– Sensitivity 75-85%– Gold standard is still culture

– Children <2m excluded from using dipstick

Question• In children <2yrs old [P] how useful is urine dipstick [I]

compared to urine culture [C] in diagnosing urinary tract infection [O]

• Paper: Schroder et al (2015) Diagnostic accuracy of the Urinalysis for Urinary tract infection in Infants <3 months age. Pediatrics (135) 965-971

Accounting for patients

Stats• Fisher or Chi squared test to compare populations

• Sensitivity/ specificity calculated for 2 samples• ‘Given that the sensitivity and specificity of the UA were

calculated in 2 separate samples of patients, likelihood ratios and predictive values would be misleading and were not calculated, and receiver operator characteristics curves were not created’.

Results

• 4 bacteremic UTIs had only trace Leu

• 1 infant had completely negative dip

Author discussion points• All but 1 of 203 patients had something on dipstick

• 2 postulations– Other studies re: urinalysis flawed by faulty gold standard – eg

contaminated urines– Spectrum bias – screening tests more sensitive when disease is

more severe

• Quotes recent study of 770 infants <3m with UTI– Dipstick sens 90%– Dipstick + microscopy 95%

Author conclusion• The UA is highly sensitive in young infants with

bacteremic UTI. Although this finding may reflect spectrum bias, it is also consistent with previous studies, suggesting that the suboptimal sensitivity of the UA may be explained by urine culture results that do not reflect true UTI

Article appraisal- validity• Was each test interpreted without knowing the results of

the other?– No. Dipstick interpreted knowing that culture was positive

• Is the spectrum of patients appropriate?– Appropriate age.– Note exclusions. – What about urine positive blood Cx negative?

• Did all patients have both tests?• Yes

• Were methods for performing test described in enough detail to permit replication– Yes

Article appraisal - results• Is sensitivity and specificity given

– Yes

• Can you construct a 2x2 table?• Are liklihood ratios given?

– Not given.– Data interpretation not done by authors given ‘2 separate

samples of patients’

Article appraisal – change management?• Can you reproduce the test locally?• Can you interpret results?

• Yes

• Are the results applicable to my patient?– Similar setting– Patient population also includes those excluded– Does not include lower UTIs

• Will results change management– Requesting further tests?– Recommending treatment?

• Will the patient be better off as a result of the test?

Unclear. Does not directly compare vs microscopy so do not know which is better

Ideal study design to answer question?• Prospective• Look at all children under 2ys for whom a microscopy is

requested• Dip urine at time of collection/ in lab

• Stats looking at microscopy and dipstick results vs positive cultures

Thank you

– Questions?