Diagnostic Paracentesis Guidelines
Initial Laboratory Tests
- A diagnostic paracentesis should include neutrophil count, total protein, albumin, and bedside inoculation of ascitic fluid into blood culture bottles as the standard initial laboratory tests, according to the European Association for the Study of the Liver 1, 2
- Cell count with differential is essential to diagnose spontaneous bacterial peritonitis (SBP) with a neutrophil count >250 cells/mm³ as the diagnostic threshold, as recommended by the American Association for the Study of Liver Diseases 3, 4, 5
Core Laboratory Tests
- Total protein concentration helps assess risk of SBP (values <1.5 g/dL indicate increased risk) and aids in differential diagnosis, as stated by the European Association for the Study of the Liver 2, 6
- Albumin is required to calculate the serum-ascites albumin gradient (SAAG), which differentiates portal hypertension-related ascites (SAAG ≥1.1 g/dL) from other causes with 97% accuracy, according to the American Association for the Study of Liver Diseases 4, 7
- Bacterial culture, specifically bedside inoculation of 10 mL of ascitic fluid into blood culture bottles, significantly improves culture yield (from approximately 50% to >80-90%), as recommended by the Infectious Diseases Society of America 2, 5, 8
Additional Tests
- Cytology should be ordered when malignancy is suspected, with a sensitivity of 96.7% when three samples are processed promptly, as stated by the American Association for the Study of Liver Diseases 8
- Glucose and LDH should be ordered when secondary bacterial peritonitis is suspected, with glucose <50 mg/dL or ascitic LDH higher than serum LDH suggesting secondary peritonitis, according to the European Association for the Study of the Liver 3
Interpretation Algorithm
- First, assess for infection by checking neutrophil count >250 cells/mm³, which indicates SBP, as recommended by the American Association for the Study of Liver Diseases 4, 2
- Second, determine the cause of ascites by calculating SAAG, with SAAG ≥1.1 g/dL indicating portal hypertension (97% accuracy), according to the European Association for the Study of the Liver 4, 9
- Third, assess additional parameters based on clinical context, such as low ascitic protein (<1.5 g/dL) indicating increased risk for SBP, as stated by the European Association for the Study of the Liver 2
Diagnostic Approach to Paracentesis
Initial Laboratory Tests
- The American Association for the Study of Liver Diseases recommends that patients with cirrhosis and ascites who are hospitalized emergently for any reason should undergo diagnostic paracentesis, even in the absence of symptoms suggestive of infection, with a neutrophil count >250 cells/mm³ indicating spontaneous bacterial peritonitis (SBP) 10, 11
- Bacterial culture should be performed by bedside inoculation of at least 10 mL of ascitic fluid into blood culture bottles, which increases culture sensitivity to >90%, and obtaining simultaneous blood samples for culture increases the possibility of isolating a causative organism in cases of suspected infection 10
- Ascitic amylase should be measured when there is clinical suspicion of pancreatic disease, as recommended by the European Society of Gastrointestinal Endoscopy 12
Indications for Diagnostic Paracentesis
- Patients with ascites who develop signs, symptoms, or laboratory abnormalities suggestive of infection (fever, abdominal pain, encephalopathy, AKI, peripheral leukocytosis) should undergo diagnostic paracentesis, with a high index of suspicion for SBP 11
- In patients with tense ascites and acute kidney injury (AKI), a diagnostic paracentesis is recommended to exclude SBP as a cause of the AKI, as suggested by the International Ascites Club 11