Uremia is a clinical syndrome associated with fluid, electrolyte, and hormone imbalances and metabolic abnormalities, which develop in parallel with deterioration of renal function. The term uremia, which literally means urine in the blood, was first used by Piorry to describe the clinical condition associated with renal failure. Uremia more commonly develops with chronic renal failure (CRF) or the later stages of chronic kidney disease (CKD), but it also may occur with acute renal failure (ARF) if loss of renal function is rapid. As yet, no single uremic toxin has been identified that accounts for all of the clinical manifestations of uremia. Toxins, such as parathyroid hormone (PTH), beta2-microglobulin, polyamines, advanced glycosylation end products, and other middle molecules, are thought to contribute to the clinical syndrome.