Evaluation of Ascites

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History and Physical Examination

The presence of ascites can usually be determined with a high degree of accuracy by history and physical examination. The most common symptom of ascites is an increase in abdominal girth accompanied by weight gain, frequently with lower extremity edema. Patients should be questioned about the risk factors for, symptoms associated with, and family history of liver disease.

A full bulging abdomen should prompt percussion of the flanks. If the degree of flank dullness is more than usual, then one should check for shifting. Flank dullness implies the presence of at least 1,500 mL of ascitic fluid. A fluid wave may be present with tense ascites, but this is not a very useful physical finding. Abdominal ultrasound, with a detection limit of 100 mL, may be required to confirm the presence of a small amount of ascites.

Physical findings are helpful in determining the etiology of ascites. Vascular spiders, splenomegaly, and engorged abdominal collateral veins suggest cirrhosis. Peripheral edema due to liver disease is usually confined to the lower extremities and may occasionally involve the abdominal wall.

Diagnostic Paracentesis and Ascitic Fluid Analysis

Paracentesis should be performed on all patients with new onset, clinically apparent ascites. Diagnostic paracentesis should be repeated if a patient develops fever, abdominal pain or tenderness, hypotension, encephalopathy, renal failure, peripheral leukocytosis, or acidosis. The prevalence of ascitic fluid infection was 10 to 27% at the time of hospital admission in the past. With effective prevention (see below), this is less common now. Hence, surveillance paracentesis on admission is warranted to exclude a subclinical infection.

Ascitic fluid analysis often establishes a definitive diagnosis. The initial routine screening tests consist of albumin, total protein, cell count, and culture. serum ascites albumin gradient (SAAG) is calculated by serum albumin-ascitic fluid albumin. This is widely used to categorize ascites. Patients with significant PHT have a SAAG a 1.1 g/dL, whereas those without PHT have a SAAG < 1.1 g/dL. SAAG predicts the presence or absence of PHT with 97% accuracy. Table 113-1 summarizes the use of SAAG, ascitic fluid total protein (AFTP), and other assays in differentiating the causes of ascites.

The cell count is the most important test for ascitic fluid infection. Ascitic fluid polymorphonuclear leukocyte (PMN) count is a much more reliable indicator of infection than the ascitic fluid white blood cell (WBC) count. Leakage of blood into the peritoneal cavity from a traumatic tap can falsely elevate the ascitic fluid PMN count. To correct for this, one PMN is subtracted from the absolute ascitic fluid PMN count for every 250 red blood cells. Patients with a corrected ascitic fluid PMN count > 250 cells/mm3 should be treated for ascitic fluid infection. In the setting of spontaneous bacterial peritonitis (SBP),

TABLE 113-1. Differentiation of Ascites Using Ascitic Fluid Tests

Causes of Ascites

SAAG (g/dL)

AFTP (g/dL)

Other Abnormalities

Cirrhotic ascites

a 1.1

Usually < 2.5

AFTP can be > 2.5 during diuresis

Cardiac ascites

a 1.1

> 2.5

Peritoneal carcinomatosis

< 1.1

> 2.5

Malignant cells in AF

Tuberculosis peritonitis

< 1.1

> 2.5

WBC > 500/mm3, lymphocyte predominance

Chylous ascites

< 1.1

> 2.5

Milky, AF triglycerides > 200 mg/dL

Nephrotic syndrome

< 1.1

< 2.5


Pancreatic ascites

< 1.1

> 2.5

AF amylase (usually > 1,000 U/L) > serum amylase

AF = ascitic fluid; AFTP = ascitic fluid total protein; SAAG = serum-ascites albumin gradient; WBC = white blood cells.

AF = ascitic fluid; AFTP = ascitic fluid total protein; SAAG = serum-ascites albumin gradient; WBC = white blood cells.

the PMN count usually constitutes over 70% of the ascitic fluid WBC count and falls dramatically after antibiotic treatment is initiated.

Culturing ascitic fluid as if it were blood gives the highest yield. Bedside inoculation of 10 to 20 mL of ascitic fluid into each of 2 culture bottles has become the standard technique, with a detection rate of over 90%. Additional testing on the ascitic fluid includes glucose, lactate dehydrogenase, amylase, triglycerides, bilirubin, and cytology. Ascitic fluid and serum levels of cancer antigen 125 are almost invariably elevated in patients with cirrhosis and ascites and should not be used as surveillance markers for peritoneal carcinomatosis.

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