In an adult with new‑onset or worsening ascites of uncertain etiology, when is diagnostic paracentesis indicated, what coagulation thresholds and pre‑procedure preparations are required, how should the procedure be performed and what studies should be sent, and how should the results (e.g., spontaneous bacterial peritonitis, malignant cells) be managed?

Diagnostic Paracentesis in New-Onset Ascites

Indications for Diagnostic Paracentesis

Perform diagnostic paracentesis immediately in every patient with new-onset ascites, regardless of symptoms. 1, 2

• All hospitalized cirrhotic patients with ascites require paracentesis on admission, even without infection symptoms. 1
• Repeat paracentesis urgently in patients who develop fever, abdominal pain or tenderness, encephalopathy, gastrointestinal bleeding, shock, renal failure, acidosis, or peripheral leukocytosis. 1
• Outpatients with worsening ascites or any concerning symptoms also require diagnostic paracentesis. 1

Pre-Procedure Coagulation Management

Do not routinely correct coagulopathy before paracentesis—prophylactic fresh frozen plasma or platelets are not recommended. 1, 2

• Paracentesis is safe despite abnormal coagulation parameters: in one large series, no hemorrhagic complications occurred despite platelet counts as low as 19,000/mm³ (54% had counts <50,000) and INRs as high as 8.7 (75% had INR >1.5). 1
• Complications occur in only ~1% of procedures, primarily minor abdominal wall hematomas. 1, 2
• The only contraindication is clinically evident disseminated intravascular coagulation or overt fibrinolysis (occurs in <1 per 1,000 procedures). 2
• Bleeding complications are disproportionately seen in patients with renal failure due to qualitative platelet dysfunction, not coagulopathy per se. 2

Procedural Technique

The preferred site is the left lower quadrant: 3 cm (two finger breadths) cephalad and 3 cm medial to the anterior superior iliac spine. 1

• This location has thinner abdominal wall and larger fluid pools compared to the midline. 1
• Avoid the right lower quadrant if there is cecal distension from lactulose or an appendectomy scar. 1
• Avoid visible collateral vessels and the inferior epigastric arteries (which run midway between the pubis and anterior superior iliac spine, then cephalad in the rectus sheath). 1
• For diagnostic purposes, withdraw 10–20 mL of fluid; for bacterial culture, inoculate ≥10 mL into blood culture bottles at the bedside before any antibiotics are given. 1, 2, 3

Mandatory Initial Laboratory Studies

Order these core tests on every first paracentesis: 1, 2, 3

1. Cell count with differential (automated methods are accurate and acceptable) 1, 2
2. Ascitic fluid albumin and simultaneous serum albumin to calculate the serum-ascites albumin gradient (SAAG) 1, 2, 3
3. Ascitic fluid total protein 1, 2, 3
4. Bacterial culture via bedside inoculation of ≥10 mL into blood culture bottles (increases yield from ~50% to 80–90%) 1, 2, 3

Interpretation of Core Results

Neutrophil Count: Diagnosing Spontaneous Bacterial Peritonitis

An ascitic fluid neutrophil count ≥250 cells/mm³ is diagnostic of spontaneous bacterial peritonitis (SBP) and mandates immediate empirical antibiotic therapy without waiting for culture results. 1, 2

• Start intravenous cefotaxime 2 g every 8 hours immediately. 1
• Choice of antibiotic should consider local resistance patterns and whether infection is community-acquired or healthcare-associated. 1
• Even patients with neutrophil counts <250 cells/mm³ but with fever (≥100°F) or abdominal pain should receive empirical antibiotics while awaiting cultures. 1
• SBP is present in approximately 15% of cirrhotic patients with ascites on hospital admission. 1

SAAG: Determining Portal Hypertension

A SAAG ≥1.1 g/dL indicates portal hypertension with 97% accuracy. 1, 2, 3

• SAAG <1.1 g/dL suggests non-portal-hypertensive causes: malignancy, tuberculosis, nephrotic syndrome, or pancreatic disease. 1, 2
• The SAAG has replaced the outdated exudate/transudate classification. 2

Total Protein: Risk Stratification

Ascitic fluid total protein <1.5 g/dL identifies patients at high risk for developing SBP and guides decisions about prophylactic antibiotics. 1, 2, 3

Optional Studies Based on Clinical Suspicion

Order these selectively when specific diagnoses are suspected:

When Suspecting Secondary Bacterial Peritonitis (Bowel Perforation)

• Ascitic fluid glucose, lactate dehydrogenase (LDH), and Gram stain. 1, 3
• Glucose <50 mg/dL, LDH higher than serum LDH, or multiple organisms on Gram stain suggest secondary peritonitis requiring surgical evaluation. 1, 3
• Ascitic carcinoembryonic antigen >5 ng/mL or alkaline phosphatase >240 U/L supports gastrointestinal perforation. 2

When Suspecting Malignant Ascites (SAAG <1.1 g/dL)

• Cytology: Sensitivity is 96.7% if three samples (50 mL each) are sent fresh and processed immediately; the first sample alone is positive in 82.8%. 1
• Only order cytology when there is clinical suspicion of peritoneal carcinomatosis (history of breast, colon, gastric, or pancreatic cancer). 1

When Suspecting Cardiac Ascites

• Serum BNP or NT-proBNP: Median pro-BNP is ~6,100 pg/mL in heart failure versus ~166 pg/mL in cirrhosis. 2
• Examine for jugular venous distension to distinguish alcoholic cardiomyopathy from alcoholic cirrhosis. 2

When Suspecting Tuberculous Peritonitis

• Adenosine deaminase (ADA): Consider in patients from endemic areas or with HIV. 1
• Ascitic fluid smear for mycobacteria has ~0% sensitivity; culture sensitivity is only ~50%. 1
• Laparoscopy with biopsy and mycobacterial culture of tubercles is the most rapid and accurate diagnostic method. 1

When Suspecting Pancreatic Ascites

• Amylase: Typically >1,000 U/L or more than 6 times the serum amylase value. 1, 2

Management of Specific Results

Spontaneous Bacterial Peritonitis (Neutrophils ≥250/mm³)

• Start cefotaxime 2 g IV every 8 hours immediately (or alternative based on local resistance patterns and whether community-acquired or healthcare-associated). 1
• Administer intravenous albumin 1.5 g/kg within 6 hours of detection and 1 g/kg on day 3 to reduce renal impairment and mortality. 1
• A follow-up paracentesis at 48 hours is optional and should be considered only if clinical response is inadequate or secondary peritonitis is suspected. 1
• The neutrophil count should decrease dramatically with appropriate antibiotics in SBP; if it rises, suspect secondary peritonitis and evaluate for perforation. 1
• After recovery from SBP, start secondary prophylaxis with norfloxacin 400 mg daily or ciprofloxacin 500 mg daily. 1

Malignant Cells on Cytology

• Positive cytology indicates peritoneal carcinomatosis. 1
• Prognosis is poor; management focuses on treating the underlying malignancy and symptom control with therapeutic paracentesis as needed. 1

Secondary Bacterial Peritonitis

• If glucose <50 mg/dL, LDH higher than serum, total protein >1 g/dL, or multiple organisms are present, suspect bowel perforation. 1
• Add anaerobic coverage to the third-generation cephalosporin and obtain urgent surgical consultation for laparotomy. 1

Common Pitfalls

• Never start antibiotics before obtaining ascitic fluid for culture—this dramatically reduces culture yield. 3
• Do not withhold paracentesis due to coagulopathy or thrombocytopenia unless there is overt DIC. 1, 2
• Do not order expensive tests (cytology, mycobacterial studies) routinely; reserve them for high pretest probability scenarios. 1
• Remember that approximately 15% of ascites cases are due to causes other than cirrhosis (malignancy, heart failure, tuberculosis, nephrotic syndrome). 1
• In cirrhotic patients who develop grade 2 or 3 ascites, one-year mortality approaches 40% and two-year mortality ~50%; evaluate for liver transplantation. 2