The<unk>  or gap (SAAG) is a calculation used in medicine to help determine the cause of<unk> . The SAAG may be a better discriminant than the older method of classifying<unk>  fluid as a transudate versus exudate. The formula is as follows: :SAAG =<unk><unk>  −<unk>  level of ascitic fluid). Ideally, the two values should be measured at the same time. This phenomenon is the result of Starling's forces between the fluid of the circulatory system and ascitic fluid. Under normal circumstances the SAAG is < 1.1 because<unk>  oncotic pressure (pulling fluid back into circulation) is exactly counterbalanced by the<unk>  hydrostatic pressure (which pushes fluid out of the circulatory system). This balance is disturbed in certain diseases (such as the Budd–Chiari syndrome, heart failure, or liver cirrhosis) that increase the hydrostatic pressure in the circulatory system. The increase in hydrostatic pressure causes more fluid to leave the circulation into the peritoneal space<unk> . The SAAG subsequently increases because there is more free fluid leaving the circulation, concentrating the<unk><unk> . The<unk>  does not move across membrane spaces easily because it is a large molecule. A rare cause of<unk> , with elevated SAAG, and without change in hydrostatic/osmotic pressure is urinary bladder rupture with leakage of urine into the peritoneal space.
Serum-ascites albumin gradient
Corpulence index
BUN-to-creatinine ratio
Urea reduction ratio
Urine osmolality
Urinary cast
Euglobulin lysis time
Microalbuminuria