Serum-ascites albumin gradient
Encyclopedia
The serum-ascites albumin gap (SAAG) is a calculation used in medicine
to help determine the cause of ascites
. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate
versus exudate
.
The formula is as follows:
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.
with 97% accuracy. 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:
, tuberculosis
, and various types of cancer
.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
to help determine the cause of ascites
Ascites
Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...
. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate
Transudate
Transudate is extravascular fluid with low protein content and a low specific gravity .This is in contrast to transudate where the extracellular fluid is an ultrafiltrate of blood plasma and thus larger molecules such as proteins and cell debris are absent....
versus exudate
Exudate
An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood...
.
The formula is as follows:
- SAAG = (albuminAlbuminAlbumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...
concentration of serumBlood serumIn blood, the serum is the component that is neither a blood cell nor a clotting factor; it is the blood plasma with the fibrinogens removed...
) - (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.
High gradient
A high gradient (> 1.1 g/dL) indicates the ascites is due to portal hypertensionPortal hypertension
In medicine, portal hypertension is hypertension in the portal vein and its tributaries.It is often defined as a portal pressure gradient of 10 mmHg or greater.-Causes:Causes can be divided into prehepatic, intrahepatic, and posthepatic...
with 97% accuracy. 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
Peritoneal cavity
The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...
but leaves proteins such as albumin within the vasculature.
Important causes of high SAAG ascites (> 1.1 g/dL) include:
- high protein (>2.5): heart failure, Budd Chiari syndrome
- low protein (<2.5): cirrhosis of the liver
Low gradient
A low gradient (< 1.1 g/dL ) indicates ascites not associated with increased portal pressure, including nephrotic syndromeNephrotic syndrome
Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein from the blood into the urine....
, tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
, and various types of cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
.