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J Clin Pathol 63:823-829 doi:10.1136/jcp.2010.077990
  • Original article

Point-of-care diagnostic tests for childhood urinary-tract infection: phase-contrast microscopy for bacteria, stick testing, and counting white blood cells

  1. John D Perry2
  1. 1Department of Paediatric Nephrology, Royal Victoria Infirmary, Newcastle, UK
  2. 2Microbiology Department, Freeman Hospital, Newcastle, UK
  1. Correspondence to Dr Malcolm G Coulthard, Department of Paediatric Nephrology, Royal Victoria Infirmary, Newcastle NE1 4LP, UK; malcolm.coulthard{at}nuth.nhs.uk

  1. Contributors MGC had primary responsibility for clinical aspects of the protocol development. He was also responsible for specimen collection and all the point-of-care testing. He undertook the primary data analysis and the initial writing of the manuscript. JDP had primary responsibility for laboratory aspects of the protocol development, and shared the laboratory testing. He shared in the final data analysis and contributed to writing the manuscript. AN and TS undertook most of the laboratory analysis, and also contributed to writing the manuscript.

  • Accepted 18 June 2010

Abstract

Aim To evaluate point-of-care testing for childhood urinary-tract infections (UTI).

Method Point-of-care testing of prospectively collected sequential paired urines was compared with quantitative culture after serial dilution in 203 children, of whom 36 had UTIs. Proportionate reduction in uncertainty (PRU) plots were used to compare between methods and with published values.

Results Phase-contrast microscopy for bacteria, as with culturing a single urine and using a threshold of 105 bacteria/ml, was 100% sensitive, making it powerful to rule UTIs out. The specificity was slightly lower than urine culture (0.860 vs 0.925) except in girls >9 years where vaginal Lactobacillus contamination reduced it to 0.61, but this increased to 0.81 when ‘urethral stream’ urines were collected. Nitrite positivity is highly specific at 0.985, making it powerful at ruling UTIs in, but its low sensitivity (0.61) makes it unsafe to rule UTIs out. A PRU plot of 16 previous studies confirmed this. Though the presence of urinary white blood cells (WBC) correlates with UTI, whether tested by point-of-care of laboratory microscopy or by stick testing, the coefficient of determination is too low to make them clinically useful, alone or combined with nitrite analysis. Seventeen other studies confirmed this.

Conclusion Phase-contrast microscopy can rule out UTIs as reliably as urine culture but is immediate, which may be clinically important. To interpret positive results reliably, girls >9 years must collect a ‘urethral stream’ urine. While nitrite positivity is useful to rule UTIs in, negative results are unreliable. Urinary WBC testing has little value.

Footnotes

  • Competing interests None.

  • Ethics approval Ethics approval was provided by the Newcastle and North Tyneside Research Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.