Reduced kidney size indicates chronic kidney disease, which is some kind of cause that destroys and damages the kidney, resulting in the destruction of kidney tissues and eventually causing the kidney to shrink in size. Generally, the causes that can cause kidney volume reduction exist chronically over a long period of time. Common causes include primary chronic glomerulonephritis, diabetes, hypertension, systemic lupus erythematosus, kidney stones, renal tuberculosis, chronic pyelonephritis or congenital dysplasia, etc. Regardless of the cause, the persistence of these factors will eventually cause sclerosis of the glomerulus and fibrosis of the renal tubules, which will result in the loss of kidney function, which will appear as a reduction in kidney size on ultrasound or CT.