Serum-ascites albumin gradient

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

The serum-ascites albumin 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.

The reason for the value measurement is simple, using Starling's forces as a guide. If you think about it, when you have a small gap (i.e. <1.1) then fluid wants to equilibrate due to oncotic pressures being similar. In conditions where there is a high gradient (ie, >1.1), the fluid SHOULD stay in the circulation because of the serum oncotic pressure trying to maintain it. Despite this desire, the ascites will still accumulate secondary to the hydrostatic pressure (ie Budd-Chiari, Heart Failure or Cirrhosis) pushing the fluid into the abdomen.

Contents

Differential

High gradient

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 out 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

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

References

  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. http://jama.ama-assn.org/cgi/pmidlookup?view=long&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