What is the management algorithm for ascitic fluid?

Ascitic Fluid Analysis Algorithm

All patients with new-onset ascites require immediate diagnostic paracentesis with cell count and differential, ascitic fluid albumin and total protein, and simultaneous serum albumin to calculate the serum-ascites albumin gradient (SAAG). 1, 2, 3

Step 1: Perform Diagnostic Paracentesis

When to Tap

• All new-onset ascites (inpatient or outpatient) 1
• All hospitalized cirrhotic patients with fever, abdominal pain, encephalopathy, GI bleeding, worsening renal/liver function, hypotension, or any clinical deterioration 2
• Outpatients with known ascites presenting with any signs of infection or clinical worsening 2

Technique and Safety

• Perform in left or right lower quadrant, approximately 15 cm lateral to umbilicus, avoiding inferior/superior epigastric arteries 1
• No prophylactic fresh frozen plasma or platelets needed even with coagulopathy, as clinically significant bleeding occurs in <1/1000 procedures 1, 3
• Consider platelet transfusion only if platelet count <40,000/mm³ 1
• Withdraw 10-20 mL for diagnostic purposes 1

Step 2: Mandatory Initial Tests on ALL Samples

Core Tests (Order on Every Initial Paracentesis)

• Cell count with differential (manual or automated) 1, 2, 3
• Ascitic fluid albumin 1, 2, 3
• Simultaneous serum albumin (same day) 1, 2
• Ascitic fluid total protein 1, 2, 3
• Culture in blood culture bottles at bedside (inoculate immediately) 1, 3

Calculate SAAG

• SAAG = Serum albumin - Ascitic fluid albumin 1
• SAAG ≥1.1 g/dL = Portal hypertension (97% accuracy) 1, 2
• SAAG <1.1 g/dL = Non-portal hypertension causes 1, 2

Step 3: Interpret Cell Count for Infection

Spontaneous Bacterial Peritonitis (SBP) Diagnosis

• PMN count ≥250 cells/mm³ = SBP → Start empirical antibiotics immediately 3
• PMN count <250 cells/mm³ with fever, abdominal pain, or encephalopathy → Start empirical antibiotics while awaiting culture 1, 3
• Culture-negative neutrocytic ascites (PMN ≥250 with negative culture) → Treat identically to culture-positive SBP 2

Bacterascites

• Positive culture with PMN <250 cells/mm³ = May represent early SBP or transient bacteremia 3
• Requires clinical correlation; treat if symptomatic 4

Secondary Bacterial Peritonitis (Gut Perforation)

• Suspect when: very high PMN count, multiple organisms on culture, or poor response to antibiotics 3
• Additional tests needed: Ascitic fluid glucose, LDH, total protein 1
• Ascitic fluid CEA >5 ng/mL or alkaline phosphatase >240 units/L suggests gut perforation 1
• Order abdominal CT scan 3

Step 4: Interpret SAAG and Total Protein

High SAAG (≥1.1 g/dL) = Portal Hypertension

Common causes: 2

• Cirrhosis (most common)
• Cardiac ascites
• Budd-Chiari syndrome
• Sinusoidal obstruction syndrome

Management implications: 1, 4

• Responds to sodium restriction and diuretics 1
• Total protein <1.5 g/dL = High SBP risk → Consider prophylactic antibiotics 4, 2
• Cardiac ascites typically has total protein >2.5 g/dL (helps distinguish from cirrhotic ascites) 2

Low SAAG (<1.1 g/dL) = Non-Portal Hypertension

Common causes: 2

• Peritoneal carcinomatosis
• Tuberculous peritonitis
• Pancreatic ascites
• Nephrotic syndrome

Management implications: 1, 4

• Generally does NOT respond to sodium restriction and diuretics (exception: nephrotic syndrome may respond) 1, 4
• Must treat underlying disorder 1, 4

Step 5: Conditional Testing Based on Clinical Suspicion

Order Cytology When:

• Clinical suspicion of malignancy 1, 2
• Low SAAG with no other obvious cause 2
• Yield varies 0-96.7% depending on tumor site 2

Order Amylase When:

• Suspected pancreatic ascites 2
• Typically >1,000 IU/L or >6 times serum amylase 2

Order Adenosine Deaminase (ADA) When:

• Suspected tuberculous peritonitis 2, 3
• ADA <40 IU/L excludes TB with high accuracy 2

Order Triglycerides When:

• Milky/chylous appearance suggests chylous ascites 5

Step 6: Follow-Up Paracentesis Strategy

Repeat Paracentesis NOT Needed:

• Typical SBP with good clinical response to antibiotics 3
• Routine therapeutic paracenteses in stable patients (only need cell count) 3

Repeat Paracentesis REQUIRED:

• Atypical clinical picture, symptoms, or organisms 3
• Poor response to appropriate antibiotics 3
• Any clinical deterioration in patients with low protein ascites (<1.5 g/dL) 4

Critical Pitfalls to Avoid

• Never rely on fluid appearance alone for diagnosis; clear fluid can be infected, bloody fluid may be traumatic tap 2
• Never order CA-125 as it is elevated by ascites from any cause and has no diagnostic value 4, 2
• Never delay antibiotics waiting for culture results if PMN ≥250 cells/mm³ 3
• Recognize mixed ascites (5% of patients have ≥2 causes) 1
• Don't assume alcoholics have alcoholic liver disease; perform full diagnostic workup 1
• Creatinine level definitively distinguishes ascites from urine if there is uncertainty 2