What studies should be ordered with a paracentesis (percutaneous abdominal paracentesis)?

Essential Studies to Order with a Paracentesis

When performing a diagnostic paracentesis, essential studies should include cell count with differential, total protein, albumin (with calculation of serum-ascites albumin gradient), and bacterial culture in blood culture bottles if infection is suspected. 1

Standard Studies for All Paracenteses

First-Line Tests (Always Order)

• Cell count and differential - Essential for detecting spontaneous bacterial peritonitis (SBP); neutrophil count >250 cells/mm³ indicates SBP 1
• Total protein concentration - Helps assess risk of SBP (values <15 g/L indicate increased risk) 1
• Albumin - For calculating serum-ascites albumin gradient (SAAG) 1
• Serum albumin (drawn simultaneously) - Required to calculate SAAG 1

SAAG Interpretation

• SAAG ≥1.1 g/dL - Indicates portal hypertension (97% accuracy) 1
• SAAG <1.1 g/dL - Suggests non-portal hypertensive causes 2

Situation-Specific Studies

When Infection is Suspected

• Bacterial culture - Inoculate directly into blood culture bottles at bedside (increases yield from 50% to 80%) 1
• Gram stain - May help guide initial antibiotic therapy 1
• Glucose and LDH - Helpful to differentiate spontaneous from secondary bacterial peritonitis 1

When Malignancy is Suspected

• Cytology - 96.7% sensitivity for peritoneal carcinomatosis when three samples are sent 1
• CEA - High specificity for malignancy-related ascites 1

When Tuberculosis is Suspected

• Adenosine deaminase (ADA) - Useful for diagnosing tuberculous peritonitis 1
• Mycobacterial culture - Sensitivity approximately 50% 1

Other Specialized Tests (Based on Clinical Suspicion)

• Amylase - When pancreatic ascites is suspected 1
• Triglyceride - Values >200 mg/dL suggest chylous ascites 1
• Brain natriuretic peptide (BNP) - Helpful in cardiac ascites 1

Clinical Algorithms for Test Selection

New-Onset Ascites

1. Always order: Cell count, total protein, albumin, serum albumin
2. Add bacterial culture if any signs of infection

Serial Therapeutic Paracentesis in Known Cirrhotic Patients

1. Cell count and differential only 1
2. Additional tests not necessary unless symptoms develop

Based on Ascitic Fluid Appearance

• Turbid fluid: Consider infection or malignancy - add culture and cytology
• Milky fluid: Suggests chylous ascites - add triglyceride
• Dark brown fluid: Suggests biliary leak - add bilirubin
• Bloody fluid: Consider malignancy or recent trauma - add cytology

Important Caveats

• Routine prophylactic use of fresh frozen plasma or platelets before paracentesis is not recommended, even with abnormal coagulation parameters 1
• Coagulopathy should only preclude paracentesis in cases of clinically evident fibrinolysis or disseminated intravascular coagulation 1
• For serial therapeutic paracenteses in stable cirrhotic outpatients, full diagnostic studies may not be necessary with each procedure 1, 3
• Bedside inoculation of culture bottles significantly improves diagnostic yield for SBP compared to delayed inoculation 4
• Avoid CA125 testing in ascites as it is non-specific and elevated in all types of ascites 2

By following this systematic approach to ascitic fluid analysis, clinicians can efficiently diagnose the cause of ascites and detect complications like spontaneous bacterial peritonitis early, improving patient outcomes.