A large number of ascitic fluid tests, e.g.,
fibronectin and
cholesterol, have been proposed as helpful in detecting
malignancy as the cause of
ascites. Unfortunately, these "humoral tests of
malignancy" are nonspecific. Although the ascitic fluid concentrations of these
proteins or
protein-bound substances tend to be quite high in patients with
peritoneal carcinomatosis and low in the setting of cirrhotic
ascites, the problem is that patients with
tuberculous peritonitis, cardiac
ascites,
pancreatitis ascites, etc. usually have values in the
malignancy range, i.e., false-positive results. This can lead to an extensive search for a nonexistent
tumor, with
confusion and anxiety for patient and physician. The cytology is the single best test to order when
peritoneal carcinomatosis is suspected; its sensitivity approaches 100%. However,
peritoneal carcinomatosis is only one of several mechanisms by which
tumors can cause
ascites. No one test can be expected to detect
tumors as the cause of these diverse mechanisms of
ascites formation. The serum-
ascites albumin gradient is a helpful test in classifying ascitic fluid specimens into
portal-hypertension-related and non-
portal-hypertension-related categories. An elevated serum
alpha-fetoprotein test can be useful in raising suspicion of
hepatocellular carcinoma. Careful analysis of ascitic fluid, without measurement of "humoral tests of
malignancy," combined with information obtained from the history and physical examination, usually lead to an accurate diagnosis of the cause of
ascites.