Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (132 page)

   Ascites is a collection of free fluid in the peritoneal cavity.

   Etiology

   Chronic liver disease (infectious hepatitis and alcoholism) causes 80% of cases of ascites (see Hepatomegaly, Jaundice).

   Multiple causes, including cirrhosis, peritoneal carcinomatosis, or tuberculous peritonitis, account for 3–5% of cases.

   Carcinomatosis causes <10% of cases of ascites.

   Heart failure is responsible for <3–5% of cases, and nephritic syndrome is a rare cause of ascites.

   Cryptogenic cirrhosis may account for up to 10% of cases.

   Classification

   Ascites is currently classified as high gradient or low gradient, depending on the serum ascites albumin gradient (SAAG). Calculation of SAAG involves the difference (not the ratio) between serum values and AF values.

   
High-gradient ascites
results from portal hypertension, whether on the basis of cirrhosis or noncirrhosis. Nephrotic syndrome is an exception and will usually cause low-gradient ascites due to marked hypoalbuminemia.

   
Low-gradient ascites
usually occurs as the result of cardiac failure, malignant carcinomatosis of the peritoneum, infections (such as TB), perforation of the bowel, connective tissues diseases, SLE, and chemical inflammation as in pancreatitis.

   Laboratory Findings (Figure
5-2
)

   
Culture
: Bedside inoculation of AF in blood culture bottles has increased the positive bacterial yield to interpreted in concert with the cell count. A Gram stain should also be done.