IgA nephropathy refers to the abnormal deposition of IgA immunoglobulin in the glomeruli of patients, which causes an inflammatory response and damages the glomerular capillaries. The extent of this damage varies, so not all patients will experience swelling. If the condition is severe, causing significant proteinuria, patients may develop hypoproteinemia and consequent decrease in plasma colloidal osmotic pressure, leading to swelling. If renal failure has occurred, the kidneys' ability to excrete water decreases, which can also cause swelling. Some patients may experience swelling due to damage to the renal tubules, which increases the reabsorption capacity for water. Otherwise, patients may not show obvious swelling, such as those with only mild proteinuria and hematuria, whose clinical symptoms are not pronounced.