Proteinuria. A six-year study of normal infants, preschool, and school-age populations previously screened for urinary tract disease

Minimal change disease: a "two-hit" podocyte immune disorder?

Minimal change disease (MCD) is the most common nephrotic syndrome in children and is commonly thought to be a T-cell disorder mediated by a circulating factor that alters podocyte function resulting in massive proteinuria. We suggest that MCD is a "two-hit" disorder. As originally hypothesized by Reiser et al. in 2004, we propose that the initial hit is the induction of CD80 (also known as B7.1) on the podocyte, and that this results in an alteration in shape with actin rearrangement that alters glomerular permeability and causes proteinuria. We propose that CD80 expression may result from either direct binding of the podocyte by cytokines from activated T cells or by activation of podocyte toll-like receptors (TLR) by viral products or allergens. We further hypothesize that under normal circumstances, CD80 expression is only transiently expressed and proteinuria is minimal due to rapid autoregulatory response by circulating T regulatory cells or by the podocyte itself, probably due to the expression of factors [cytotoxic T-lymphocyte-associated (CTLA)-4, interleukin (IL)-10, and possibly transforming growth factor (TGF)-β] that downregulate the podocyte CD80 response. In MCD, however, there is a defect in CD80 podocyte autoregulation. This results in persistent CD80 expression and persistent proteinuria. If correct, this hypothesis may lead to both new diagnostic tests and potential therapeutics for this important renal disease.

Proteinuria: potential causes and approach to evaluation

Proteinuria may be associated with a renal or systemic disease, or it may be isolated. The latter occurs in asymptomatic patients without evidence of any disease or abnormality of the urine sediment. Isolated proteinuria may be subdivided into two broad groups: (1) benign forms, with a favorable-to-excellent prognosis and (2) persistent forms, some of which have a worrisome prognosis. Functional proteinuria may occur in disorders with altered renal hemodynamics, usually resolves, and is not associated with progressive renal disease. Idiopathic transient proteinuria is typically discovered on routine screening and usually disappears on subsequent testing. In idiopathic intermittent proteinuria, a significant number (50%) of urine samples exhibit abnormal rates of protein excretion. Although structural abnormalities may be observed on renal biopsy, progressive renal insufficiency is unusual. In orthostatic proteinuria, the rate of protein excretion completely normalizes in the recumbent position. Long-term studies show this to be a benign condition. In persistent isolated proteinuria, at least 80% of random urine samples exhibit abnormal protein excretion. This represents a heterogeneous group, but a significant proportion of these patients have prominent renal pathologic findings and progress to serious renal disease. Proteinuria with significant renal disease may be non-nephrotic or nephrotic range. The former does not exclude glomerular disease, but tubulointerstitial or vascular disorders are also likely when proteinuria is less than 2 g/24 hours. Patients with nephrotic-range proteinuria generally have a glomerular disorder. Distinction between benign and more ominous forms of proteinuria requires careful evaluation.

Evaluating the child with proteinuria

Proteinuria is a common laboratory finding in children. It might represent a benign condition or herald the presence of a serious underlying renal disease or systemic disorder. Investigation to confirm a diagnosis or seek reassurance is important. This paper discusses the various causes of proteinuria, and those aspects of the history, physical examination, and the laboratory tests that will help determine the cause or reassure that a serious problem is not currently present.

Evaluation of hematuria, proteinuria, and hypertension in adolescents

Signs or symptoms of renal disease in adolescents deserve prompt attention and appropriate evaluation. Adolescents are susceptible to a variety of urinary tract disorders. The key issue in the evaluation of hematuria or proteinuria in adolescents is the existence of concomitant signs of renal disease. For isolated hematuria or proteinuria, demonstration of persistence and a reasoned evaluation are in order. Hypertension in adolescents must be carefully documented and, when present, considered seriously. The fact that most teens with persistent elevated blood pressures have essential hypertension is still a great concern because for most of these adolescents the hypertension will be lifelong and, if left untreated, can be associated with significant morbidity and mortality in the adult years.

An office approach to hematuria and proteinuria

An organized practical approach for the pediatrician to use in evaluating a child with hematuria or proteinuria emphasizes common conditions and stepwise laboratory/radiologic investigations. Additional points of emphasis include when to refer to a pediatric nephrologist or urologist and when to consider renal biopsy. Real case statistics and salient examples from the major published studies should assist the pediatrician in counseling the patient and his or her family, especially when there is no medical indication to refer to a specialist.

Assessment of urinary protein excretion in the adolescent: effect of body position and exercise

We examined the effects of body position and exercise on the random urinary protein/creatinine ratio (Up/Ucr) in healthy adolescents, to provide reference data to be used in a simplified evaluation of proteinuria. Random urine samples were obtained during recumbency and after both ambulation and exercise in 116 subjects. The Up/Ucr was significantly (P less than 0.0001) higher with increasing levels of activity, and was widely variable, especially during the upright and postexercise periods. No sex-related differences in Up/Ucr were noted, except during recumbency, when values were significantly (P less than 0.001) higher in females. The urinary dipstick was found to be less sensitive as a tool to define abnormal degrees of recumbent proteinuria. We conclude that body position and exercise have significant effects on protein excretion, and suggest that the Up/Ucr in recumbent and upright urine samples will be useful in the evaluation of proteinuria.

Proteinuria in Sudanese children

One thousand, eight hundred and forty-six apparently healthy nursery and school children living in the Khartoum area and belonging to different socio-economic classes were studied. Nine hundred and thirty-seven were boys, 909 girls. Their ages ranged from three to 16 years. N-multistix strips were used to test for proteinuria and haematuria, the former being also checked by the sulphosalicylic acid test. Children with proteinuria of 1+ or more were further investigated by examining their urinary sediment for abnormal deposits and by testing for orthostatic proteinuria using day and night specimens of urine with specific gravity of 1.018 or more. Children who had no proteins on orthostatic testing were rescreened for proteinuria 10-14 days after the initial screening. The prevalence rate for proteinuria was 7.2% with no significant difference between boys and girls. In both sexes the prevalence rate increased significantly with age but was not influenced by the socio-economic status. Of the children with proteinuria, haematuria occurred in 27% and abnormal urinary deposits in 14.8%. Orthostatic testing showed a negative result for proteins in 44%, orthostatic proteinuria in 40%, of whom a third had either abnormal urinary sediments or haematuria, and continuous proteinuria in 15.6% of whom the majority had abnormal deposits.

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.

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.

Proteinuria in children with febrile illnesses

Transient proteinuria in the absence of underlying renal disease was detected in 11 of 198 children (5·6%) admitted to hospital with an acute febrile illness. Proteinuria was noted only in children whose fever was higher than 38·4 °C. Selectivity studies on the protein excreted showed patterns ranging from poorly to highly selective. Initial screening for proteinuria using a dipstick method revealed a high incidence of false positives, of which only about 30% could be confirmed by the sulphosalicylic acid method. The pathophysiology of transient proteinuria in febrile patients is not understood; a number of mechanisms are probably involved. Since fever was the only detected feature common to each of the patients with proteinuria, it seems unlikely that the specific aetiology of the fever is a factor of importance in the pathogenesis of the proteinuria.