What indicates glomerular filtration damage and impaired selective filtration?

Glomerular proteinuria is indicative of glomerular filtration damage because it results from an alteration in the permeability of the glomerular capillary wall. In healthy kidneys, the glomeruli selectively filter blood, allowing smaller molecules, such as water, glucose, and ions, to pass while preventing larger molecules, particularly proteins, from being excreted into the urine. When glomerular damage occurs—due to conditions such as glomerulonephritis, diabetic nephropathy, or hypertension—the filtration barrier becomes compromised, allowing larger proteins, such as albumin, to leak into the urine.

This abnormal presence of protein in the urine is a direct indicator of severe impairment in the glomerular filtration function. In contrast, other types of proteinuria, such as tubular proteinuria, arise from damage to the renal tubules that affects the reabsorption of proteins rather than the filtration process itself. Orthostatic proteinuria generally occurs due to positional changes and is typically seen in younger individuals, while post-renal proteinuria may arise from issues in the urinary tract after filtration, rather than the glomeruli themselves. Therefore, glomerular proteinuria specifically points to direct damage to the glomeruli and impaired selective filtration.