What is the initial workup for a patient requiring paracentesis?

Initial Workup for Paracentesis

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. 1

Core Laboratory Tests

• Cell count with differential is essential to diagnose spontaneous bacterial peritonitis (SBP) with a neutrophil count >250 cells/mm³ as the diagnostic threshold 2, 1
• Total protein concentration helps assess risk of SBP (values <1.5 g/dL indicate increased risk) and aids in differential diagnosis 1, 3
• Albumin measurement 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 1, 4
• 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% 2, 1

Ultrasound Guidance

• Ultrasound guidance should be used for paracentesis to reduce the risk of serious complications, particularly bleeding 5
• Ultrasound should be used to assess the volume and location of intraperitoneal free fluid to guide clinical decision making of where paracentesis can be safely performed 5
• The needle insertion site should be evaluated using color flow Doppler ultrasound to identify and avoid abdominal wall blood vessels along the anticipated needle trajectory 5
• The needle insertion site should be marked with ultrasound immediately before performing the procedure, and the patient should remain in the same position between marking the site and performing the procedure 5

Additional Tests Based on Clinical Context

• Cytology should be ordered when malignancy is suspected, with a sensitivity of 96.7% when three samples are processed promptly 1
• Glucose and LDH should be ordered when secondary bacterial peritonitis is suspected (glucose <50 mg/dL or ascitic LDH higher than serum LDH suggesting secondary peritonitis) 1
• Ascitic amylase should be measured when there is clinical suspicion of pancreatic disease 2

Indications for Diagnostic Paracentesis

• All patients with new-onset ascites should undergo diagnostic paracentesis 4
• 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 2
• Patients with ascites who develop signs, symptoms, or laboratory abnormalities suggestive of infection (fever, abdominal pain, encephalopathy, AKI, peripheral leukocytosis) should undergo diagnostic paracentesis 2, 4
• In patients with tense ascites and acute kidney injury (AKI), a diagnostic paracentesis is recommended to exclude SBP as a cause of the AKI 2

Interpretation Algorithm

1. First, assess for infection by checking neutrophil count >250 cells/mm³, which indicates SBP 2, 1
2. Second, determine the cause of ascites by calculating SAAG, with SAAG ≥1.1 g/dL indicating portal hypertension (97% accuracy) 1, 6
3. Third, assess additional parameters based on clinical context, such as low ascitic protein (<1.5 g/dL) indicating increased risk for SBP 3

Common Pitfalls and Caveats

• Obtaining simultaneous blood samples for culture increases the possibility of isolating a causative organism in cases of suspected infection 2
• Antibiotics should not be started before obtaining cultures, as this significantly reduces the yield of bacterial cultures 2
• Bacterascites (positive culture but neutrophil count <250 cells/mm³) requires clinical correlation and may represent early SBP in symptomatic patients 3
• CA-125 in serum or ascites has no role as a discriminator and will commonly be elevated by the presence of ascites from any cause 3
• Routine correction of prolonged prothrombin time or thrombocytopenia is not required when experienced personnel carry out paracentesis 7