What studies should be ordered for a patient presenting with ascites?

Diagnostic Studies for Ascites

A diagnostic paracentesis with appropriate ascitic fluid analysis is essential in all patients with ascites prior to any therapy to determine the underlying cause and rule out complications such as spontaneous bacterial peritonitis. 1

Initial Evaluation Algorithm

Step 1: Diagnostic Paracentesis

• Perform at a site approximately 15 cm lateral to the umbilicus (left or right lower quadrant), avoiding enlarged liver/spleen and epigastric arteries 1
• Withdraw 10-20 ml of ascitic fluid for analysis 1
• No need for prophylactic fresh frozen plasma in patients with abnormal coagulation profiles (though pooled platelets may be considered if platelet count <40,000) 1

Step 2: Essential Ascitic Fluid Tests

1. Serum-ascites albumin gradient (SAAG)

   • If ≥1.1 g/dl: indicates portal hypertension (97% accuracy) 1
   • If <1.1 g/dl: indicates non-portal hypertensive cause 1

2. Total ascitic fluid protein concentration

   • Levels <15 g/L indicate increased risk of spontaneous bacterial peritonitis 1

3. Neutrophil count

   • Count ≥250 cells/mm³ is diagnostic of spontaneous bacterial peritonitis 1

4. Ascitic fluid culture

   • Inoculate 10 ml into blood culture bottles at bedside 1

Step 3: Additional Targeted Tests (When Clinically Indicated)

• Amylase: When pancreatic disease is suspected 1
• Cytology: When malignancy is suspected 1
• PCR and culture for mycobacteria: When tuberculosis is suspected 1

Additional Diagnostic Studies

Laboratory Tests

• Complete blood count
• Liver function tests
• Prothrombin time
• Renal function tests (urea, creatinine)
• Serum electrolytes 1

Imaging Studies

• Abdominal ultrasound: Essential to evaluate:
  • Liver appearance and size
  • Pancreas
  • Lymph nodes
  • Presence of splenomegaly (suggesting portal hypertension)
  • Quantification of ascites 1

Interpretation and Classification

Causes of Ascites

• Approximately 75% of ascites cases in Western countries are due to cirrhosis 1
• Other causes include:
  • Malignancy
  • Heart failure
  • Tuberculosis
  • Pancreatic disease 1

Classification of Ascites Severity

• Grade 1 (mild): Only detectable by ultrasound
• Grade 2 (moderate): Moderate abdominal distension
• Grade 3 (large): Marked abdominal distension 2

Common Pitfalls to Avoid

1. Assuming etiology without proper testing: Never assume alcoholic patients have alcoholic liver disease without proper investigation 1

2. Omitting paracentesis due to coagulopathy concerns: Paracentesis is not contraindicated in patients with abnormal coagulation profiles common in cirrhosis 1

3. Incomplete ascitic fluid analysis: Always perform the complete panel of recommended tests rather than selective testing 1

4. Delayed culture collection: Inoculate ascitic fluid into culture bottles immediately at bedside to improve diagnostic yield 1

5. Missing rare causes: While cirrhosis is the most common cause, always consider other etiologies such as malignancy, tuberculosis, and heart failure 1, 3

Follow-up Considerations

• All patients with ascites should be considered for liver transplantation evaluation 2
• Regular monitoring of ascites grade and complications is essential 2
• Screen for hepatocellular carcinoma at diagnosis and every 6 months thereafter 2

By following this systematic approach to diagnostic studies for ascites, clinicians can accurately determine the underlying cause and guide appropriate management strategies to improve patient outcomes.