Fixed and reproducible orthostatic proteinuria. VI. Results of a 10-year follow-up evaluation

Beginning the trajectory to ESKD in adult life: albuminuria in Australian aboriginal children and adolescents

BACKGROUND

Globally, disadvantaged populations suffer a high burden of chronic kidney disease (CKD). The trajectory to CKD during childhood and adolescence remains unclear due to a paucity of longitudinal studies.

METHODS

This was a prospective, population-based cohort study in which since 2002 we have followed 3418 children (1469 non-Aboriginal and 1949 Aboriginal) attending participating schools across New South Wales (NSW), Australia. The albumin:creatinine ratio was measured by dipstick every 2 years together with the body mass index (BMI) and blood pressure. We used multivariable logistic generalised estimating equation models to examine whether Aboriginal children had a higher prevalence of albuminuria compared with non-Aboriginal children with increasing age and to identify potential risk factors.

RESULTS

The mean age at enrolment was 10.6 years, at which time 14.2 % of the children were obese and 16.0 % overweight, with 11.5 % found to have albuminuria. Over 8 years (11,387 participant-years) of follow-up the prevalence of albuminuria increased to 18.5 %, overweight to 16.1 % and obesity to 17.2 %. The BMI standard deviation score (SDS) was found to have a differential effect on the risk of albuminuria in Aboriginal and non-Aboriginal children (P interaction < 0.01). The prevalence of albuminuria decreased as the BMI SDS increased in both groups of children, but it increased more in non-Aboriginal children, leading to a 2.5 % higher prevalence of albuminuria in overweight Aboriginal children (95 % confidence interval 1.0-4.2 %).

CONCLUSION

Compared with non-Aboriginal children, Aboriginal children are of higher risk of albuminuria when overweight or obese. We hypothesise that overweight and obesity are key contributors to the development of adult onset CKD among Aboriginal Australians, which needs further exploration in future studies.

Asymptomatic constant isolated proteinuria in children

The clinical features, renal biopsy findings, and subsequent course in 53 children with asymptomatic constant isolated proteinuria were studied retrospectively (1) to determine the prevalence of renal pathologic abnormalities among these children, (2) to identify those clinical characteristics that may enable recognition of children with an increased likelihood of having renal pathologic abnormalities, and (3) to assess the clinical course. All biopsy specimens were examined by light, immunofluorescence, and electron microscopy. Twenty-five patients (47%) had significant glomerular changes (15 had focal segmental glomerulosclerosis, 4 IgA nephropathy, 3 diffuse mesangial proliferative glomerulonephritis without IgA deposition, and 3 membranous glomerulonephritis), and 28 had minimal glomerular changes. There were no differences between the patients with significant glomerular changes and those with minimal glomerular changes with regard to clinical and laboratory findings except for a predominance of boys in the former group. At the latest follow-up, seven patients with significant glomerular changes, but none with minimal glomerular changes, had chronic renal impairment. Because of the high incidence of significant glomerular changes and the high rate of progression to chronic renal impairment, we believe that a renal biopsy is indicated for a child with asymptomatic constant isolated proteinuria.

The prognostic significance of proteinuria: the Framingham study

Despite considerable clinical experience with proteinuria, its prognostic meaning in the ambulatory general population is poorly documented. From a 16-year study of 5209 men and women in the Framingham cohort it is evident that proteinuria, even in casual urine specimens, carries substantial risk with the mortality rate increased threefold. Proteinuria was three times as common in hypertensive persons and also occurred to excess in diabetic patients and in persons with cardiac enlargement. In the absence of these factors, proteinuria was so uncommon that its risk could not be accurately assessed. Among persons with these associated risk factors, those with proteinuria have higher death rates than those without proteinuria. In men, overall mortality and cardiovascular mortality rates remained significantly increased even when other contributors to risk were taken into account. Proteinuria in the ambulatory general population is not a benign condition and carries a serious prognosis. It appears to reflect widespread vascular damage.

Proteinuria in children. Review and evaluation

Current information relating to the clinical significance of proteinuria in children through adolescence was reviewed. Proteinuria may be transient, orthostatic, or fixed. The data indicate that only fixed proteinuria-that is, proteinuria on multiple urine examinations without postural exaggeration-may indicate serious glomerular disease. The patient should be followed with periodic but infrequent examinations, avoiding unnecessary, complicated, and hazardous investigations.

Isolated proteinuria: analysis of a school-age population

Proteinuria was found in at least one of four specimens in 10.7% and in at least two of four specimens in 2.5% of 8,594 schoolchildren, ages 8 to 15 years. To determine the risk of renal disease in isolated proteinuria, the screening program was followed by a systematic clinical evaluation of the proteinuric children. After those with both proteinuria and hematuria were excluded, none of the remaining children was found to have an overt renal disease. Despite urinary protein concentrations in excess of 1,000 mg/dl and protein excretion rates of up to 1 gm in 24 hours, proteinuria proved to be transient or intermittent in every child when a large enough number of urine samples was tested. Children with the highest protein excretion rates (more than 6 mg/hour/m2 at night or more than 20 mg/hour/m2 during the day) and those with the most persistent patterns of proteinuria underwent renal function studies, intravenous pyelography, and renal biopsy. No significant abnormalities was found. Mild nonspecific changes were seen in 12 of 28 biopsies, with mesangial deposits in four. The results show that if hematuria and other signs have been excluded, a benign renal morphologic picture is almost invariably to be expected in intermittent proteinuria; renal biopsy, therefore, is not indicated.

Renal biopsy findings in orthostatic proteinuria

Percutaneous renal biopsy was performed on 15 patients with orthostatic proteinuria and 6 control subjects without proteinuria in order to investigate possible renal alterations. The light-microscopic findings were either normal or showed slight mesangial proliferation in the orthostatic group but were normal in the control subjects, while the immunofluorescence-microscopic study revealed mesangial, capillary or arteriolar deposits of complement C3 and/or immunoglobulins in 10 out of 12 cases with orthostatic proteinuria; complement C3 was seen in only one control subject. The electron-microscopic findings were similar in the two groups, showing slight subepithelial, intramembranous and mesangial alterations. Focal loss of the epithelial foot processes was seen in only one case with orthostatic proteinuria. It is concluded that there are no histological, electron microscopical or immunohistochemical alterations specific for orthostatic proteinuria. A finding of complement in the glomeruli in about half and of immunoglobulin in some of the patients with orthostatic proteinuria is in favour of an association to present or previous glomerulonephritis.

Renal dysfunction. 2. Proteinuria

Proteinuria greater than 150 mg/24 hr without antecedent strenuous exercise demands an explanation. As an aid in the search for that explanation, this article provides a simple, logical classification of the various causes of proteinuria. Part 1 of this two-part article, published last month (page 93), discussed urea and creatinine.

Selectivity as a clue to diagnosis of postural proteinuria

In 14 patients with fixed and reproducible postural proteinuria and 14 patients with histologically proven glomerulonephritis, the selectivity of proteinuria was measured separately in the day and night urine collections. The selectivity of proteinuria in the urine collected in recumbency was lower in patients with glomerulonephritis than in patients with postural proteinuria. All patients with postural proteinuria showed an increment of the selectivity from day to night of at least 13 degrees, whereas the maximum increment in patients with glomerulonephritis was 5 degrees. The changes in selectivity from day to night in patients with postural proteinuria and patients with glomerulonephritis were significantly different and seem to be a useful discriminatory test.

Proteinuria and hematuria in schoolchildren: epidemiology and early natural history

Over the past several decades screening for disease in large asymptomatic populations has increased, culminating most recently with a federal mandate for early, periodic screening, diagnosis and treatment of all children from low-income families. The present study of five consecutive examinations in over 12,000 schoolchildren shows the cumulative occurrence of proteinuria and hematuria to be surprisingly high (greater than 6%). Comparison of this large number of children with the few individuals in whom death occurs from chronic renal disease annually (less than 0.03%) suggests that the vast majority of these children with urinary abnormalities have either no renal disease or at most a self-limited condition. Observation of 512 children with proteinuria and 78 with hematuria for one to five years after initial detection and referral to their physician or clinic provides a measure of both contemporary management and early natural history. These observations suggest that there is a need to question the overall effectiveness of urinary screening and that early inclusion of roentgenographic and urologic investigations in management seems unwarranted. Rather, these children should be followed for long periods of time. Additional investigations are indicated when worsening of the abnormal findings or other evidence of renal or systemic disease occurs. If routine urinary screening is performed, it should be as one aspect of a multiphasic program by the primary physician so that it can be coupled with a clearly defined plan for follow-up and management of subjects with abnormal findings.