Bacteriuria, reflux, and renal scarring

Much of the confusion in the discussion of these topics reflects differences of nomenclature not of fact, and a failure to relate the wide variation in severity both of reflux and of renal damage to their long-term implications. In this article, significant bacteriuria denotes the presence of actively multiplying organisms in the urinary tract and is indicated in girls by a pure growth of at least 105 organisms/ml on culturing two consecutive clean, fresh specimens of urine. Lesser counts may be significant in boys, as is any growth on culture of bladder urine obtained by suprapubic aspiration. Reflux is the backflow of urine from bladder to ureter. It is considered to be abnormal and varies in aetiology, severity, and prognosis. The 'renal damage' discussed is the scarring of chronic pyelonephritis, which is recognizable morphologically and radiologically by the irregular distribution of coarse scars with deformity or frank clubbing of a calyx directly associated with thinning of the overlying renal tissue. There is usually a reduction in renal size (Hodson, 1965). (Some authors have classified as chronic pyelonephritis kidneys which fail to show all three of these features and this has made the comparison of different studies more difficult.) The regular association of these findings with reflux has led to the introduction of the term 'reflux nephropathy' (Bailey, 1973), but until the precise mechanical role of reflux is more firmly established the use of the term 'chronic pyelonephritis' is perhaps preferable. Chronic pyelonephritis varies in degree from the unilateral single polar scar to more extensive scarring (which if bilateral may lead to impaired renal function), and to the small shrunken kidney usually found to have severe associated reflux and often hypertension. The association of bacteriuria with renal scarring is well known. Up to 25% of such children investigated, whether seen in hospital or discovered during screening programmes, are found to have some degree of renal scarring though this is likely to be of serious significance in no more than 10%. 20% of the University College Hospital series of children with chronic pyelonephritis had raised blood pressure and 10% had some degree of renal failure (Smellie et al., 1975). Similarly, children with coarsely scarred kidneys almost invariably have reflux. In a few, established chronic pyelonephritis has been reported in the absence of reflux, but in these the possibility that previously existing reflux had already disappeared cannot be excluded. The occasional persistence of paraureteric saccules or the finding of patulous ureteric orifices on cystoscopy in such children support this view. However, vascular, mechanical, or immunological factors as well as infection may contribute to the formation and progression of renal scars; and hypertension, obstruction, or areas of renal dysplasia as well as reflux may be important in individual children.