Diagnostics

• Indications

  • Clinical suspicion of new-onset ascites

  • Evaluation for an underlying condition (e.g., cirrhosis, intraabdominal malignancy) [8]

  • Ultrasound-guided paracentesis

• Supportive findings

  • Free intraperitoneal fluid

    • Uncomplicated nonhemorrhagic ascites typically appears hypoechoic/anechoic

    • Internal echoes, debris, and septations are suggestive of exudates. [7]

  • Features of underlying etiology (e.g., liver cirrhosis, hepatocellular carcinoma, Budd-Chiari syndrome, portal vein thrombosis, ovarian tumors; see respective articles for details)

• Indications: to work up for the underlying cause as needed; examples include

  • GI perforation in patients with postoperative or traumatic ascites

  • Secondary peritonitis

  • Malignancy

• Findings

  • Free intraperitoneal fluid

  • Fluid density depends on the type of ascites

The choice of laboratory studies should be guided by the pretest probability of the suspected underlying etiology.

• CBC: abnormalities related to an underlying condition

• Coagulation panel: Thrombocytopenia and coagulopathy are signs of advanced liver disease.

• Liver chemistries

  • Elevated transaminases suggest liver disease.

  • Serum albumin (for SAAG calculation)

• BMP

  • Elevated creatinine and BUN: Acute kidney injury is common in patients with decompensated cirrhosis. [9]

  • Serum electrolytes: hypervolemic hypotonic hyponatremia (as a complication of cirrhosis) [10]

• Additional evaluation for the underlying condition

• All patients with new-onset ascites (to identify the underlying etiology)

• To detect spontaneous bacterial peritonitis (SBP) or other peritoneal infections in the following situations:

  • Clinical features of SBP

  • Hospitalization for any cause in patients with cirrhosis and ascites (to identify occult SBP)

• Gross appearance: can provide supportive evidence of the underlying cause or complications

  • Transparent to yellow: uncomplicated ascites

  • Cloudy: infection or malignancy

  • Bloody: trauma or malignancy

  • Milky: chylous ascites

  • Dark brown: suggestive of a biliary leak (e.g., gallbladder perforation)

• Cell count and differential: A neutrophil count ≥ 250 cells/mm3 indicates spontaneous bacterial peritonitis.

• Ascitic fluid albumin: for SAAG calculation (obtain same-day serum and ascitic fluid samples)

• Ascitic fluid total protein

  • To differentiate cirrhosis from cardiac etiologies in high SAAG ascites

  • To differentiate SBP (typically ≤ 1 g/dL) from secondary peritonitis (typically > 1 g/dL

• Suspected infection

  • Microbiology: ascitic fluid culture in blood culture bottles (aerobic and anaerobic) and Gram stain

  • Studies to differentiate SBP from secondary spontaneous peritonitis: LDH, glucose, CEA, alkaline phosphatase

  • Acid-fast bacilli smear and mycobacterial cultures (low sensitivity): only if there is clinical suspicion or a high risk of tuberculous peritonitis

• Suspected malignancy (e.g., peritoneal carcinomatosis)

  • Ascitic fluid cytology

  • Ascitic fluid tumor markers: not routinely recommended for the assessment of malignancy-related ascites

    • Cancer antigen 125 (CA-125): elevated in most patients with ascites regardless of etiology

    • Carcinoembryonic antigen (CEA): potentially of diagnostic and prognostic value in patients with gastric and intestinal carcinoma

• Suspected chylous ascites (milky ascitic fluid): Ascitic fluid triglyceride levels; levels > 200 mg/dL indicate chylous ascites

• Suspected pancreatic ascites or bowel perforation: Ascitic fluid amylase levels; elevated levels provide supportive evidence of pancreatitis or bowel perforation