Occurrence of renal scars in children after their first referral for urinary tract infection

Introduction

Urinary tract infections in childhood may cause renal scars, which can lead to hypertension and renal failure: diagnostic imaging is therefore important to detect children with scarring so that they can be monitored. A multidisciplinary group that produced imaging guidelines1 broadly agreed that younger children should have a dimercaptosuccinic acid (DMSA) scan to detect scarring and an ultrasonography to identify structural lesions after one infection, but most thought that children over 7 years should be investigated only after recurrent infections, using ultrasound only, perhaps because of their low risk of new scar formation.2 Others have suggested imaging only children who have a fever.3 In Newcastle we have performed ultrasound and dimercaptosuccinic acid scans (after two months free of infection) on every child when first referred after a urinary tract infection. Here we describe our referral and scarring rates.

Patients, methods, and results

We calculated first referral rates for urinary tract infections in children aged under 16, from three health districts, from scan records at the Royal Victoria Infirmary and Newcastle General Hospital throughout 1992-5. Details available for the Royal Victoria Infirmary's cases (81%) included sex, age, extent of scarring, and consultant. Details of the presenting infections were obtained from clinical notes (92 children with scars, 232 controls), including bacteriological evidence, history, associated fever, vomiting, malaise or anorexia, hospital admission, and ultrasound findings.

The mean annual referral rate was 0.46% (2842 children in 4 years, from a population of 154 000). Girls outnumbered boys threefold; cumulative referral rates by the age of 16 were 3.6% for boys and 11.3% for girls (1). Under 1 year boys and girls were seen in similar numbers, but deviated thereafter. Sex and age profiles remained stable through the study, but referrals rose by half, reaching 4.5% for boys and 14.4% for girls by 1995. The scarring rate was similar in boys and girls, at 4.3% and 4.7%, and did not alter during the study (χ² test for trend, P=0.23). Logistic regression showed no association with sex (P=0.77) or age (P=0.46; 1). Of the children with scars, 54% had multiple lesions. There was no evidence of selective referral of patients likely to have scarring; paediatric nephrologists rather than general paediatricians were referred 48.8% of the cases and identified 45.1% of the scars. Between half and three quarters of infants were febrile; had vomiting, anorexia, or malaise; and required hospital admission. These rates all fell to less than a third in children over 4. Neither these indicators nor a history suggesting previous urinary tract infections were of value for predicting scarring. Ultrasound coincidentally identified some of the scars.

Comment

Our cumulative referral rates for urinary tract infections are fairly high but similar to those of other recent studies.4 They might be overestimates because 15% of diagnoses were not bacteriologically proved, or underestimates through failure to diagnose or refer. Our rising referral rate may reflect increased awareness. We were surprised that the scarring rate was similar at about 5% regardless of sex, age, symptoms, or history. Scars being commoner in girls presumably reflects girls' greater susceptibility to urinary infections. Scars identified in older children are presumably the result of unrecognised infections when younger. To improve diagnosis rates in infants it would be necessary to collect a urine sample from every infant with an unexplained illness,1 now feasible with urine collection pads.5 Since there is an equal chance of diagnosing a scar in a teenager after a urinary tract infection as there is in a toddler, there is equal merit in screening with a dimercaptosuccinic acid scan (ultrasound alone being insufficient). Children aged 4 and older with normal images can be discharged safely.2