Lupus nephritis is a serious complication of systemic lupus erythematosus (SLE) in which the immune system attacks the kidneys, causing inflammation and damage to the glomeruli (the filtering units of the kidneys). It affects up to 50% of lupus patients, often within the first few years of diagnosis.

Symptoms may include proteinuria, hematuria, swelling (edema) in the legs or around the eyes, and sometimes high blood pressure or reduced kidney function. It is diagnosed through urinalysis, blood tests, and often a kidney biopsy, which helps determine the class and severity.

Early detection and aggressive treatment are critical to prevent progression to kidney failure.