Stress Tolerance Test and SDS-PAGE for the Analysis of Urinary Proteins in Children and Youths

Abstract

Excretion of urinary proteins (UP) is an important marker for the evaluation of patients with progressive renal disease. In order to analyze quantitative and qualitative variability of UP in relation to physical activity, we used standardized stress tolerance test and SDS-PAGE. Five urine samples were obtained from each patient at rest, during ordinary daily activity and after physical stress. Determination of total proteins was performed using Meulman's classic method with sulfosalicylic acid. UP were separated by ultrathin horizontal gradient SDS-PAGE according to Görg. There were 142 patients; 40 with poststreptococcal glomerulonephritis (PSGN), 11 with diabetes mellitus, 16 with chronic pyelonephritis and 75 who attended for investigation of asymptomatic proteinuria. Functional proteinuria was established in 42 subjects, who displayed maximal UP excretion during stress and the presence of apolipoprotein AI on SDS-PAGE. Children with PSGN showed no significant increase of UP during stress. Some children with diabetes mellitus (27%) and chronic pyelonephritis (47%) displayed microproteinuria or overt proteinuria after stress. Quantitative and qualitative changes in total UP excretion can be detected by stress tolerance test and SDS-PAGE. It remains to be seen whether stress tolerance test can identify children and youths who are at higher risk for disease progression.

The Spectrum of Kidney Diseases in Children Associated with Low Molecular Weight Proteinuria

“…Before the treatment of a child with proteinuria, functional (orthostatic) proteinuria should be excluded [ 2 ] [ 3 ] [ 4 ] [ 5 ]. It is characterised by excretion of proteins only in postural position.…”

“…If this processing shows normal results, only annual audits are sufficient. SDS-PAG electrophoresis is an elegant method where the presence of Apolipoprotein A1 fraction (APO-A1) with a molecular mass of 28 KD is a pathognomonic sign for orthostatic proteinuria [ 2 ] [ 3 ].…”

“…It is a method that was developed during the 90s of the last century. The advantage is that a panoramic view of all proteins is obtained, so a clear classification of the type of proteinuria is possible [ 1 ] [ 2 ] [ 3 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ]. It is relatively fast and inexpensive method; it is possible to analyse multiple samples, especially using the Phast system [ 21 ].…”

Low Molecular Weight Proteinuria in Children with Distal Renal Tubular Acidosis

“…We have successfully used it for differentiation of glomerular from non-glomerular hematurias and for analysis of functional proteinurias (orthostatic, exercise induced proteinuria). [19,20,21] Analysis of the elepherograms enables pan-oramic investigation of various fractions according to their molecular weight and more subtle characterization of proteinuria (e.g. non selective glomerular with incomplete tubular proteinuria).…”