Ascites and pleural fluid

Published on 02/03/2015 by admin

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Last modified 02/03/2015

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64

Ascites and pleural fluid

Ascites

Serum-ascites albumin gradient

The serum-ascites albumin gradient (SAAG) is defined as the serum albumin concentration minus the ascitic fluid albumin concentration. The SAAG correlates directly with the portal pressure. Patients with a wide SAAG (defined as ≥11 g/L) have portal hypertension, whereas patients with a narrow SAAG (<11 g/L) do not (Table 64.1).

Table 64.1

Serum-ascites albumin gradient

Wide (>11 g/L) Narrow (<11 g/L)
Chronic liver disease (cirrhosis) Peritoneal carcinomatosis
Veno-occlusive disease Reduced plasma oncotic pressure (e.g. nephrotic syndrome)
Massive hepatic metastases Secondary peritonitis
Congestive cardiac failure Tuberculous peritonitis
Spontaneous bacterial peritonitis  

Sometimes causes of ascites that are normally associated with a narrow gradient will occur in patients with portal hypertension, in which case the gradient will be wide. In these situations additional analyses may assist with the differential diagnosis. For example, abnormalities of pH, lactate, glucose and/or lactate dehydrogenase (LDH) may point towards an inflammatory process; increased lymphocytes in the ascitic fluid may point towards tuberculosis, lymphomas or fungal infections of the peritoneum; and malignant cells are found in nearly all patients with peritoneal carcinomatosis (where the tumour directly involves the peritoneum).

Peritonitis

Cirrhotic patients with ascites are prone to develop peritonitis, usually without an obvious focus of infection (so-called spontaneous bacterial peritonitis or SBP). Less commonly, identifiable sources of infection, e.g. perforated viscus or intra-abdominal abscess, are responsible (secondary infection). Laboratory investigations can assist in three ways. First, they may be used to predict who is going to develop SBP. Second, they may permit rapid detection of infection. Third, they may help to differentiate SBP from secondary infection.

Early detection

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