Renal failure is categorized into pre-renal (red), intrinsic (blue), and post-renal (yellow) disease. Pre-renal disease results from reduced blood supply to the renal tissue mainly due to cardiovascular changes, which decreases glomerular filtration rate and, consequently, induces cellular damage. Intrinsic disease is the result of direct cellular injury to the kidney and can be categorized based on the location of the damage (glomerular, vascular, tubular or interstitial). Post-renal disease can be extrarenal or intrarenal and it is usually caused by obstructive uropathy.