From their recent study, Sood et al. concluded that a negative urinary nitrate test can be used to exclude urinary tract infection (UTI) in children where possibility of UTI is low(1). However, only 20% of the samples in this study were from children and no age stratified data on the study population is given. Dipsticks have been extensively tested in adults and older children and have been found to be a useful screening test. But it less useful in screening for UTI in infants and young children(2,3). Unfortunately this is precisely the age group where UTI should not be missed. In infants and young children bacteriuria associated with vesicoureteric reflux may lead to irreversible kidney damage and scarring and therefore diagnosis of UTI has far reaching implications. The results of this study therefore, cannot be used for making recommendation on screening for UTI in children.

Several factors influence the sensitivity of nitrates for picking up UTI in infants and toddlers. Collection of a midstream clean catch of urine is extremely difficult in this age group. Often catherisation, suprapubic aspiration or collection from clean pads is required. In order to allow bacterial enzyme sufficient time to release nitrite, the bacteria should be in contact with urine in the bladder for minimum of 4 hours. Therefore a random urine sample will have much less sensitivity than a first morning specimen. Frequent voiding of urine by young children, further makes it difficult.

I recently screened 50 consecutive children admitted to the children’s ward with dipstick testing and compared it with culture(3). Nitrates were found to have a very high specificity (92.4%) for detecting UTI. However, sensitivity of nitrates was very low even when combined with Leucocyte esterase (64.5%). It was seen that if four parameters (blood, protein, leucocyte esterase and nitrates) are combined and if the urine is sent for culture if any of these is abnormal, the sensitivity increased to 96.9% (negative predictive value 97.7%) and the chance of missing UTI became very small. UTI in children cannot be excluded by a negative dipstick nitrates and Leucocyte esterase enzyme. However, I agree with the authors that a positive urinary nitrate can be used to start early antibiotic therapy if UTI is suspected, because irreversible changes in kidney are known to occur within 48 hours of the onset of infection.

Sudhin Thayyil-Sudhan,
Neonatal Unit, Leicester Royal Infirmary,
55 Hospital Close, Evington,
Leicester LE5 4WQ, UK
E-mail: [email protected]

1. Sood S, Upadhyaya P, Kapil A, Lodha R, Jain Y, Bagga A. An indigenously developed nitrite kit to aid in the diagnosis of urinary tract infection. Indian Pediatr 1999; 36: 887-890.

2. Shaw KN, McGowan KL, Gorelick MH, Schwartz JS. Screening for urinary tract infec-tion in infants in the emergency department: Which test is the best? Pediatrics 1998; 101: 1065-1068.

3. Thayyil Sudhan S, Gupta S. Dipstick examina-tion for urinary tract infection in children. To screen or not to screen? Arch Dis Child (in press).

 

Dr. Thayyil-Sudhan highlights the limita-tions of urine nitrite as a screening test for the diagnosis of urinary tract infections. His concerns are valid, particularly when the test is applied to small children. We agree wih his observation, given the low sensitivity of the test that ranges from 21-50%(1–3).

Keeping the limitations of the nitrite test in mind, we are in the process of combining detection of leukocyte esterase activity, urine nitrite and microscopy for screening children for urinary infections. Although he reports a low sensitivity of the combined nitrite and leukocyte esterase test(4), there are others who claim an overall negative predictive value of the combined dipstick test of 98%(1).

We do appreciate that the screening tests may not detect all urinary tract infections in children below two years of age. However, we believe that the number of urinary infections that we will miss after combining nitrite, leukocyte esterase and microscopy will be small. A satisfactory screening test would definitely reduce the work load in a clinical microbiology laboratory, where at least 80% of the samples are cultured unnecessarily every day. Also, we would like to highlight at this point that our intent is to develop a diagnostic system for use in areas where culture facilities are not available or standardized. We would also like to mention that dipsticks in these set ups are unaffordable.

Lastly, we emphasize that the urinary dipsticks test for nitrite, and not nitrates (contrary to what Dr. Thayyil–Sudhan mentions in his letter).

Seema Sood,
Department of Microbiology,
All India Institute of Medical Sciences,
Ansari Nagar, New Delhi 110 029, India.

1. Shaw KN, Hexter D, McGowan KI, Schwartz JS. Clinical evaluation of a rapid screening test for urinary infections in children. J Pediatr 1991; 118: 733-735.

2. Goldsmith BM, Campos JM. Comparison of urine dipstick, microscopy and culture for the detection of bacteriuria in children. Clin Pediatr 1990; 29: 214-218.

3. Lohr JA, Portilia MG, Gender TG, Dunn ML, Dudley SM. Making a presumptive diagnosis of urinary tract infection by using urinalysis performed in an on-site laboratory. J Pediatr 1993; 122: 22-25.

4. Thayyil Sudan S, Gupta S. Dipstick examination for urinary tract infection in children. To screen or not to screen? Arch Dis Childhood (in press).