How to Cite This Chapter: Ghent SA, De Freitas K, Wong A, Khalid Z, Juszczyk J. Ascites. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed April 24, 2024.
Last Updated: March 12, 2020
Last Reviewed: July 19, 2021
Chapter Information

Definition, Etiology, PathogenesisTop

Ascites is defined as an excessive accumulation of fluid in the abdominal cavity (definitions differ, but the difference is not clinically relevant).

1. Key mechanisms: Increased hydrostatic portal pressure, decreased blood oncotic pressure, excessive fluid production, impaired lymphatic drainage.

2. Etiology: Table 1.

3. Classification of ascites by fluid volume:

1) Mild ascites (grade 1) is detectable only by ultrasonography.

2) Moderate ascites (grade 2) can be detected on physical examination. The fluid volume is usually >500 mL.

3) Severe ascites (grade 3) causes abdominal distension accompanied by flattening of the umbilicus or umbilical hernia. Dyspnea indicates that the peritoneal fluid volume is large, up to ~5 to 15 L.


1. History and physical examination may reveal both the presence of ascites and features of the underlying condition. Clinical manifestations include abdominal distension, which may be associated with discomfort, dyspnea, early satiety, and weight gain.

Physical examination may include a number of tests, but it should be noted all of them have limited accuracy:

1) A positive fluid wave indicates a 5-fold increase in the odds of ascites, whereas a negative fluid wave decreases these odds by half.

2) The presence of shifting dullness increases the odds of ascites 2.3-fold, whereas its absence decreases these odds by more than half.

3) Flank dullness and the presence of peripheral edema have similar limiting properties.

Physical examination may also reveal stigmata of chronic liver disease.

Features suggestive of portal hypertension as the cause of ascites are distension of the veins of the abdominal wall due to the development of portosystemic collateral circulation (communication between the umbilical vein and the veins of the abdominal wall or between the inferior mesenteric vein and the perirectal plexus) and splenomegaly. A small firm liver is suggestive of cirrhosis, while a rough and hard liver is suggestive of cancer.

2. Diagnostic studies:

1) Imaging studies: Ultrasonography and computed tomography (CT) confirm the presence of fluid in the peritoneal cavity, determine its volume, and are used to evaluate the liver for size, structure, and focal lesions. These studies also detect features of portal hypertension, spleen enlargement, and abnormalities of other abdominal organs.

2) Examination of ascitic fluid (obtained by paracentesis [see Abdominal Paracentesis]): Calculating the serum-to-ascites albumin gradient (SAAG) is useful in differentiating exudative causes (usually <11 g/L) from transudative causes (≥11 g/L). The following can be used as complementary tests to exclude other causes: measurements of total protein, glucose, triglycerides, bilirubin, lactate dehydrogenase, and amylase; analysis of the number and type of cells (diagnosis of spontaneous bacterial peritonitis, cancer cells); and cultures (in patients with suspected spontaneous bacterial peritonitis or tuberculosis).


Treatment of the underlying condition. Therapeutic paracentesis (see Abdominal Paracentesis) is performed when indicated.


Table 1.1-1. Causes of ascites



Increased hydrostatic portal hypertension

Cirrhosis (~80%), heart failure, Budd-Chiari syndrome


Nephrotic syndrome, protein-losing nephropathy, malnutrition

Peritoneal disease

Tumors (~10%), chlamydial peritonitis, systemic lupus erythematosus, portal vein thrombosis, Meigs syndrome (benign ovarian tumor with ascites and pleural effusion)


Chylous ascites, pancreatitis, myxedema, hemoperitoneum from trauma

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