Serum-ascites albumin gradient

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Pathophysiology sample values
Na+ = 140Cl = 100BUN = 20/
Glu = 150
K+ = 4CO2 = 22PCr = 1.0\
HCO3- = 24paCO2 = 40paO2 = 95pH = 7.40
pACO2 = 36pAO2 = 105A-a g = 10
Ca = 9.5Mg2+ = 2.0PO4 = 1
CK = 55BE = −0.36AG = 16
PMO = 300PCO = 295POG = 5BUN:Cr = 20
UNa+ = 80UCl = 100UAG = 5FENa = 0.95
UK+ = 25USG = 1.01UCr = 60UO = 800
LDH = 100TP = 7.6AST = 25TBIL = 0.7
ALP = 71Alb = 4.0ALT = 40BC = 0.5
AST/ALT = 0.6BU = 0.2
AF alb = 3.0SAAG = 1.0SOG = 60
CSF alb = 30CSF glu = 60CSF/S alb = 7.5CSF/S glu = 0.4

The serum-ascites albumin gradient or gap (SAAG) is a calculation used in medicine to help determine the cause of ascites.[1] The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate versus exudate.[2]

The formula is as follows:

SAAG = (albumin concentration of serum) - (albumin concentration 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 serum oncotic pressure (pulling fluid back into circulation) is exactly counterbalanced by the serum 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 (ascites). The SAAG subsequently increases because there is more free fluid leaving the circulation, diluting the albumin in the ascitic fluid. The albumin does not move across membrane spaces easily because it is a large molecule.


High gradient[edit]

A high gradient (> 1.1 g/dL) indicates the ascites is due to portal hypertension with 97% accuracy.[2] This is due to increased hydrostatic pressure within the blood vessels of the hepatic portal system, which in turn forces water into the peritoneal cavity but leaves proteins such as albumin within the vasculature.

Important causes of high SAAG ascites (> 1.1 g/dL) include:

Low gradient[edit]

A low gradient (< 1.1 g/dL ) indicates causes of ascites not associated with increased portal pressure. Examples include tuberculosis, pancreatitis, nephrotic syndrome and various types of peritoneal cancer.


  1. ^ Wong CL, Holroyd-Leduc J, Thorpe KE, Straus SE (March 2008). "Does this patient have bacterial peritonitis or portal hypertension? How do I perform a paracentesis and analyze the results?". JAMA 299 (10): 1166–78. doi:10.1001/jama.299.10.1166. PMID 18334692. 
  2. ^ a b Runyon BA, Montano AA, Akriviadis EA, Antillon MR, Irving MA, McHutchison JG (August 1992). "The serum-ascites albumin gradient is superior to the exudate-transudate concept in the differential diagnosis of ascites". Annals of Internal Medicine 117 (3): 215–20. PMID 1616215. 
  3. ^ Gines P, Cardenas A, Arroyo V, Rodes J. Management of cirrhosis and ascites. N Engl J Med. 2004 15;350:1646-54. PMID 15084697