Differentials
Secondary peritonitis
SIGNS / SYMPTOMS
Much rarer than SBP as a cause of infected ascitic fluid should be suspected when localized abdominal symptoms or signs, presence of multiple organisms on ascitic culture, very high ascitic neutrophil count and/or high ascitic protein concentration, or in those patients with an inadequate response to therapy.[64] Secondary peritonitis may cause more rigidity and the patients are usually, overall, appear much more ill. Sepsis is common in these patients. Have a higher suspicion if history of intestinal perforation, abdominal surgery, or small bowel or if there is no history of liver disease or malignancy.
Typically not the large-volume distention seen with ascites caused by liver disease or malignancy and therefore associated with SBP.
INVESTIGATIONS
Polymicrobial growth on ascitic fluid culture, which is particularly suggestive of secondary peritonitis if there is an anaerobic or fungal organism.
Ascitic fluid is more likely to have increased protein and lactate dehydrogenase with reduced glucose.[109]
Ascitic fluid is more likely to have increased carcinoembryonic antigen and alkaline phosphatase.[98]
There is less likely to be a decreased absolute neutrophil count on repeat paracentesis.[112] CT abdomen should be considered to confirm diagnosis and cause in high-risk patients.[64]
Tuberculous peritonitis
SIGNS / SYMPTOMS
There may be extra-abdominal signs and symptoms of tuberculosis (pleural, pulmonary, CNS, bony, genitourinary). Abdominal symptoms may be very similar to those of SBP.
INVESTIGATIONS
The definitive test is peritoneal biopsy with examination for granulomas.
Acid-fast staining of ascitic fluid is not a good differentiator, because it is negative in up to 92% of patients with peritoneal tuberculosis.[113]
CT scan may show enlarged abdominal lymph nodes.
Adenosine deaminase level >39 units/L is highly suggestive of peritoneal tuberculosis.[114]
Intraperitoneal hemorrhage into ascitic fluid
SIGNS / SYMPTOMS
Signs of hemorrhagic shock may be present. A history of a recent large-volume paracentesis may be a clue to hemorrhage. Abdominal pain and distention may be similar to SBP.
INVESTIGATIONS
The presence of grossly bloody ascitic fluid on paracentesis, especially if prior paracentesis did not demonstrate hemorrhagic ascites, is suggestive of intraperitoneal hemorrhage.
Pancreatic ascites
SIGNS / SYMPTOMS
There may be a history of previous pancreatitis. Abdominal symptoms and signs may be difficult to differentiate from SBP.
INVESTIGATIONS
Peritoneal fluid absolute neutrophil count likely to be normal.
Amylase is typically elevated (>1000 units/L), and the ratio of ascitic fluid amylase to serum amylase is approximately 6.[115]
In a case series of 8 patients with pancreatic ascites, ascitic fluid amylase values ranged from 280 to 5730 units/L.[116]
The serum albumin-ascites albumin gradient (SAAG) is usually <1.1 g/dL, whereas in SBP (which typically occurs in the patient with portal hypertension), SAAG is >1.1 g/dL.
CT scan may demonstrate a pancreatic pseudocyst.
Choleperitoneum (rupture of gallbladder into peritoneum)
SIGNS / SYMPTOMS
It should be suspected with bile staining of ascitic fluid (dark orange or brown color).
INVESTIGATIONS
If bile staining of ascitic fluid consider measuring ascitic fluid bilirubin concentration. If both ascites bilirubin >6 mg/dL and ascites : serum bilirubin ratio >1.0 this is very suggestive of choleperitoneum. If ascitic fluid amylase obtained, normal amylase would suggest upper gastrointestinal perforation rather than gallbladder perforation.
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