British Journal of Radiology 74 (2001),331-334 © 2001 The British Institute of Radiology
Vesicoureteric reflux and renal scarring in Chinese children
R G Howard, FRANZCR
D J Roebuck, FRCR, FRANZCR
P Au Yeung, FRCR, FHKCR
K W Chan, FRCR, FHKCR
and
C Metreweli, FRCR, FRCP
Department of Diagnostic Radiology, Prince of Wales Hospital, Sha Tin, Hong Kong
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Abstract
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Vesicoureteric reflux (VUR) and renal scarring are commonly found in children with urinary tract infection (UTI). The prevalence of VUR and scarring may vary between racial groups. There are no published data on the prevalence of VUR and scarring in Chinese children with UTI. A retrospective, single-institution study was made of Hong Kong Chinese children aged less than 5 years with a documented UTI investigated by both micturating cystourethrography and dimercaptosuccinic acid scintigraphy. VUR was identified in 39% of 93 Chinese children with UTI. Renal scarring was present in 28% of boys, which is comparable with published data on Western children. Scarring appears to be less common in Chinese girls with UTI (11%) than in Western girls (30–38% from published data), and its severity is poorly related to VUR grade. There is a significant dependency relationship between grade of VUR and degree of scarring in Chinese boys (p<0.05). In conclusion, renal scarring appears to be relatively uncommon in Chinese girls. The correlation between grade of VUR and degree of scarring in Chinese boys suggests a relationship, but provides no evidence about the direction of causation.
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Introduction
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The occurrence of vesicoureteric reflux (VUR) and renal scarring in children with urinary tract infection (UTI) has been well documented. Various studies suggest that the prevalence of VUR and scarring may be different in different racial groups. In particular, the prevalence of VUR and scarring in Black children with UTI appears to be lower than in White children [1–3].
The association between VUR and scarring isalso well documented. Several studies in Caucasian children and one study in Japanese children have shown a relationship between the degree of scarring and the grade of VUR [4–7].
No report of the prevalence of VUR and scarring in Chinese children, or the existence of any dependency relationship between these phenomena, has been published in the international literature. The aim of this study was to obtain this information.
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Methods
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We identified all Chinese children aged less than 5 years who had presented to our institution with a documented UTI from 1994 to 1999, and who had undergone both micturating cystourethrography (MCU) and dimercaptosuccinic acid scintigraphy (DMSA).
All DMSA studies had been performed at least 3 months after, and all MCU studies at least 6 weeks after any known UTI. The radiographs from the MCU studies were reviewed and any VUR was graded using the international (five grade) system [8]. The DMSA studies were examined for the presence and severity of scarring. This was done by dividing each kidney into three regions of approximately equal size (upper pole, mid portion and lower pole) and recording the presence of scarring in each region. The kidney was then scored as follows: normal=0; focal scarring in one region=1; scarring involving two regions=2; scarring involving all three regions=3; and generalized reduction in cortical mass=4 (Figure 1
). Examples of the scoring system are shown in Figure 2. To our knowledge, this particular technique has not been used before.
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Figure 2. Examples of the renal scarring scoring system. (a) Normal left kidney, grade 1 scarring at the lower pole of the right kidney. (b) Grade 2 scarring in the right kidney, grade 3 in the left. (c) Grade 4 scarring in the left kidney.
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The dependency relationship between VUR and renal scarring was calculated using the contingency test.
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Results
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93 children were identified, 65 of them male. The prevalence of VUR was 39% (45% in males and 25% in females), and the prevalence of scarring was 23% (28% in males and 11% in females).
Two children had a solitary functioning kidney, leaving 184 renal units for analysis. VUR was demonstrated in 55 renal units (Table 1). There was a significant dependency relationship (p<0.05) between the degree of scarring and the grade of VUR. When the renal units were categorized by sex, a significant dependency relationship was seen between the degree of scarring and the grade of VUR for boys (p<0.05) (Figure 3), but this was not shown to be significant for girls.
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Table 1. Scarring score and grade of vesicoureteric reflux (VUR) in 184 renal units of 93 Chinese children with urinary tract infection
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Figure 3. Correlation between mean scarring score and grade of vesicoutreteric reflux (VUR) in 129 renal units of 65 Chinese boys with urinary tract infection.
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Discussion
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The prevalence of VUR in children with UTI appears to vary with geographical location (Table 2). To some extent this may reflect racial differences, as can be seen from the studies comparing different groups in the same location [1–3]. However, there are likely to be confounding variables that have not been controlled for in these studies. In general, the effect of race on the prevalence of VUR can only be surmised.
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Table 2. The prevalence of vesicoureteric reflux (VUR) as detected by micturating cystourethrography in children with urinary tract infection, by geographical location
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Kunin [1] and Askari and Belman [2] found prevalences of VUR in Black American children with UTI of 9% and 12%, respectively. A recent study by Melhem and Harpen [3] confirmed this, finding VUR in less than 10% of Black children of all age groups. The published data for the prevalence of VUR in White children with UTI vary from 21% to 63% [9–14]. In our study, the prevalence of VUR in Chinese children with UTI was 39% (45% in boys, 25% in girls). This is comparable with that seen in White children.
The prevalence of renal scarring as detected by DMSA in European and Australian children with UTI has been reported as varying from 27% to 42% [9–11, 13, 15] (Table 3). An earlier study showed a lower rate of scarring, at 21% [16]. However, this study used intravenous urography (IVU) to detect renal scars. This method is believed to be less sensitive than DMSA, which has been used in the more recent studies. None of these studies divided their patients into racial groups. Another early paper implied that scarring was not present in Black girls with bacteriuria [1], but this study also relied on IVU for scar detection.
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Table 3. Prevalence of renal scarring as detected by dimercaptosuccinic acid scintigraphy (DMSA) in children with urinary tract infection, by different geographical location
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We detected renal scarring in 23% of Chinese children with UTI. This is at the low end of the range of published results for other groups. Our rate of scar detection in boys was 28%, and this is within the calculated 95% confidence interval for Western children (Table 3
). In girls, however, the prevalence of scarring (11%) fell below the 95%confidence interval for Western children (30–38%), suggesting that scarring in Chinese girls with UTI is significantly less common than in European or Australian girls.
In boys, there was a clear relationship between the grade of VUR and the degree of scarring for each renal unit (Table 1; Figure 3). This suggests that the association between these findings is not coincidental. Several interpretations are possible: scarring may cause VUR; VUR may cause scarring; some other factor may cause both; or more than one of these mechanisms may apply. Similar results have been found in Western children [6, 9, 10].
There was no significant dependency relationship between the grade of VUR and the degree of scarring for girls. This finding may not definitely indicate that there is no relationship between VUR and renal scarring in Chinese girls, because the numbers involved (55 renal units) are relatively small, and this study may not have the statistical power to detect a dependency relationship. As has been noted before, several children in this study, both male and female, showed evidence of renal scarring at DMSA without detectable VUR at MCU.
In this study the incidence of VUR and scarring was calculated for individual children with UTI and not for renal units. This was because most of the previous papers, and in particular those mentioning racial differences, presented their figures in a similar way and direct comparison was therefore possible.
It should be noted however, that the information presented in terms of renal units may be more meaningful than that for individual patients and this could be a subject for further research.
As always in retrospective studies of this nature, the possibility of bias must be considered. In particular, the children included in this study do not represent an unbiased sample of all Chinese children with UTI. The method of investigation of patients with UTI at our institution has not been standardized, and the children identified by this study probably represent a more severely affected subgroup because they were referred for more intensive radiological investigation.
However, similar selection bias was also present in all of the identified papers. In general, the more severely affected cases tended to be included in the studies. For example, two studies included only cases of febrile UTI, one involving temperatures above 38.5 °C only [10, 14]. One paper only included those patients referred for DMSA [13]. Also, several papers included only those patients referred to their paediatric hospital for investigation, which probably selects more severely affected patients [9, 11, 12, 15]. This may limit the validity of generalization from this and other papers.
In conclusion, the prevalence of VUR in Chinese children with UTI (39%) and the prevalence of scarring in Chinese boys (28%) are comparable with published data from Western populations. However, the prevalence of scarring in Chinese girls with UTI (11%) is significantly lower than for Western girls (30–38%). There is no significant dependency relationship between grade of VUR and degree of scarring in Chinese girls, whereas the dependency relationship in boys is significant.
Received for publication January 6, 2000.
Revision received December 19, 2000.
Accepted for publication January 24, 2001.
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Abstract
Introduction
