The serum-ascites albumin gradient or gap (SAAG) is a calculation used in

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

to help determine the cause of

ascites Ascites (; , meaning "bag" or "sac") is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdo ...

. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a

transudate Transudate is extravascular fluid with low protein content and a low specific gravity (< 1.012). It has low nucleated cell counts (less than 500 to 1000 per microliter) and the primary cell types are mononuclear leukocyte, mononuclear cells: macrop ...

versus

exudate An exudate is a fluid released by an organism through pores or a wound, a process known as exuding or exudation. ''Exudate'' is derived from ''exude'' 'to ooze' from Latin language, Latin 'to (ooze out) sweat' (' 'out' and ' 'to sweat'). Medi ...

. The formula is as follows: :SAAG = ( serum

albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All of the proteins of the albumin family are water- soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Alb ...

) − (albumin 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 < 1.1g/dL (11g/L) 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 Budd–Chiari syndrome is a condition when an occlusion or obstruction in the hepatic veins prevent normal outflow of blood from the liver. The symptoms are non-specific and vary widely, but it may present with the classical triad of abdomin ...

, 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, concentrating the serum albumin. The albumin does not move across membrane spaces easily because it is a large molecule. A rare cause of ascites, with elevated SAAG, and without change in hydrostatic/osmotic pressure is urinary bladder rupture with leakage of urine into the peritoneal space.

Differential

High gradient

A high gradient (> 1.1 g/dL, >11 g/L) indicates the ascites is due to

portal hypertension Portal hypertension is defined as increased portal venous pressure, with a hepatic venous pressure gradient greater than 5 mmHg. Normal portal pressure is 1–4 mmHg; clinically insignificant portal hypertension is present at portal pressures 5� ...

, either liver related or non-liver related, with approximately 97% accuracy. This is due to increased

hydrostatic pressure Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...

within the blood vessels of the

hepatic portal system In human anatomy, the hepatic portal system or portal venous system is a system of veins comprising the portal vein and its tributaries. The other portal venous system in the body is the hypophyseal portal system. Structure Large veins that ar ...

, which in turn forces water into the

peritoneal cavity The peritoneal cavity is a potential space located between the two layers of the peritoneum—the parietal peritoneum, the serous membrane that lines the abdominal wall, and visceral peritoneum, which surrounds the internal organs. While situated ...

but leaves proteins such as albumin within the vasculature. Important causes of high SAAG ascites (> 1.1 g/dL, >11 g/L) include:

cirrhosis of the liver Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, chronic liver failure or chronic hepatic failure and end-stage liver disease, is a chronic condition of the liver in which the normal functioning tissue, or parenchyma, is replaced ...

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

portal vein thrombosis Portal vein thrombosis (PVT) is a vascular disease of the liver that occurs when a blood clot occurs in the hepatic portal vein, which can lead to increased pressure in the portal vein system and reduced blood supply to the liver. The mortality ...

, and idiopathic portal fibrosis.

Low gradient

A low gradient (< 1.1 g/dL, <11 g/L) indicates causes of ascites not associated with increased portal pressure such as:

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

pancreatitis Pancreatitis is a condition characterized by inflammation of the pancreas. The pancreas is a large organ behind the stomach that produces digestive enzymes and a number of hormone A hormone (from the Ancient Greek, Greek participle , "se ...

infections An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

serositis Serositis refers to inflammation of the serous tissues of the body, the tissues lining the lungs (pleura), heart (pericardium), and the inner lining of the abdomen (peritoneum) and organs within. It is commonly found with fat wrapping or creepin ...

, various types of peritoneal

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

s (peritoneal carcinomatosis) and

pulmonary infarct Lung infarction or pulmonary infarction occurs when an artery to the lung becomes blocked and part of the lung dies. It is most often caused by a pulmonary embolism. Because of the dual blood supply to the lungs from both the bronchial circulati ...

References

{{reflist Medical tests Hepatology