Ascitic Fluid Analysis

What is ascites?

Ascites is the accumulation of ascitic fluid in the peritoneal cavity.

Many diseases can cause ascites, but the most common is portal hypertension, which is usually due to cirrhosis.

Ascites does not typically become clinically detectable until there are at least 500mLs of fluid present.

If large amounts of fluid accumulate, the abdomen can become very distended and tense, causing the patient to feel short of breath (due to diaphragmatic splinting).

Analysis of ascitic fluid can help determine the underlying cause and identify signs of infection.

A sample of fluid is typically obtained using a needle and syringe (known as an “ascitic tap” or “paracentesis”) and sent for analysis.


Signs and symptoms of ascites

  • Abdominal distension
  • Abdominal discomfort
  • Weight gain
  • Shortness of breath
  • Reduced appetite

Appearance of ascitic fluid

Ascitic fluid appearance
Ascitic fluid appearance


Ascitic fluid biochemistry

Ascitic fluid biochemistry
Ascitic fluid biochemistry

Ascitic fluid microscopy

Ascitic fluid microscopy
Ascitic fluid microscopy

Serum Ascitic Albumin Gradient (SAAG)

The Serum Ascitic Albumin Gradient (SAAG) indirectly measures portal pressure and can be used to determine if ascites is due to portal hypertension.

SAAG calculation

SAAG = (Serum albumin) – (Ascitic fluid albumin)

A high SAAG (>1.1g/dL) suggests the ascitic fluid is a transudate.

A low SAAG  (<1.1g/dL) suggests the ascitic fluid is an exudate.


A high SAAG (i.e. transudate) suggests the presence of portal hypertension:

  • Cirrhosis
  • Hepatic failure
  • Venous occlusion e.g. Budd Chiari syndrome
  • Fulminant hepatic failure
  • Alcoholic hepatitis
  • Kwashiorkor malnutrition

NB: A transudate commonly results from increased pressure in the portal vein.


Causes of a low SAAG (i.e. exudate) include:

  • Malignancy
  • Infection
  • Pancreatitis
  • Nephrotic syndrome

NB: An exudate commonly results from inflammation or malignancy.


An alternative way of differentiating between an exudate and transudate is using lactate dehydrogenase activity (LDH), which is also measured from ascitic fluid.

  • LDH <225 U/L = transudate
  • LDH > 225U/ L = exudate

This has largely been replaced by the use of SAAG.



Andrew Gowland



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