What testing should be done for a patient with sudden onset ascites and right upper quadrant pain?

Diagnostic Testing for Sudden Onset Ascites with Right Upper Quadrant Pain

A diagnostic paracentesis with ascitic fluid analysis is the essential first step in evaluating sudden onset ascites with right upper quadrant pain, accompanied by abdominal ultrasound, comprehensive blood tests, and potentially CT imaging depending on initial findings. 1

Initial Diagnostic Approach

Diagnostic Paracentesis

• Required ascitic fluid tests:

  • Neutrophil count and differential (>250 cells/mm³ indicates SBP)
  • Total protein and albumin levels (protein <1.5 g/dL is risk factor for SBP)
  • Bacterial culture (bedside inoculation into blood culture bottles)
  • Serum-ascites albumin gradient (SAAG) calculation 1

• Additional ascitic fluid tests based on clinical suspicion:

  • Cytology (if malignancy suspected)
  • Amylase (if pancreatic ascites suspected, typically >1,000 mg/dL)
  • Glucose and LDH (if secondary peritonitis suspected; glucose <50 mg/dL or LDH higher than serum LDH suggests secondary peritonitis)
  • Tuberculosis testing if TB peritonitis suspected 1

Imaging Studies

• Abdominal ultrasound (first-line imaging):

  • Evaluates liver appearance, pancreas, gallbladder, and lymph nodes
  • Assesses for splenomegaly (suggesting portal hypertension)
  • High sensitivity (81%) and specificity (83%) for acute cholecystitis
  • 96% accuracy for detecting gallstones
  • No radiation exposure 1, 2

• CT abdomen with contrast (if ultrasound inconclusive):

  • Better visualization of liver, pancreas, and other abdominal organs
  • Can identify complications such as perforation or abscess
  • Superior for evaluating the extent of ascites 1, 2

Laboratory Tests

• Essential blood tests:
  • Complete blood count (evaluate for leukocytosis)
  • Liver function tests (assess liver damage)
  • Prothrombin time (coagulation status)
  • Urea and electrolytes (renal function)
  • Pancreatic enzymes (amylase, lipase) 1, 2

Additional Testing Based on Initial Findings

• If biliary obstruction or choledocholithiasis suspected:

  • MRI with MRCP (superior for detecting small stones in gallbladder neck, cystic duct, or common bile duct) 2

• If acute cholecystitis suspected but ultrasound inconclusive:

  • Tc-99m Cholescintigraphy (HIDA scan) - highest sensitivity (97%) and specificity (90%) for acute cholecystitis 2

• If cardiac cause suspected:

  • Echocardiogram
  • Brain natriuretic peptide (BNP) or pro-BNP levels 1, 3

Special Considerations

• Paracentesis technique:

  • Optimal site: 15 cm lateral to umbilicus in left or right lower quadrant
  • Avoid enlarged liver/spleen and superficial blood vessels
  • Withdraw 10-20 mL for diagnostic purposes
  • Complications rare but include bleeding (0.2-2.2%) 1

• Contraindications to paracentesis:

  • Clinically evident hyperfibrinolysis or disseminated intravascular coagulation
  • Relative contraindications: pregnancy, severe intestinal distension, extensive abdominal surgery 1

• For women of reproductive age:

  • Beta-hCG testing before imaging
  • If pregnant, ultrasound is preferred initial imaging 2

Diagnostic Algorithm

1. Perform diagnostic paracentesis with complete ascitic fluid analysis
2. Obtain abdominal ultrasound to evaluate liver, gallbladder, and other organs
3. Order essential blood tests (CBC, LFTs, PT, electrolytes)
4. Calculate SAAG to differentiate portal hypertension-related from non-portal hypertension-related ascites
5. If initial tests inconclusive:
   • CT with contrast for better visualization
   • Additional specialized testing based on clinical suspicion

Common Pitfalls to Avoid

• Don't assume alcoholic patients with ascites have alcoholic liver disease - complete evaluation is still necessary 1
• Don't delay paracentesis due to coagulopathy - paracentesis is not contraindicated in patients with abnormal coagulation profiles 1
• Don't forget to consider multiple causes of ascites - approximately 5% of patients have two or more causes 1, 3
• Don't rely solely on non-contrast CT for gallbladder evaluation - it has limitations in detecting wall enhancement patterns and early inflammation 2
• Don't miss cardiac causes of ascites - evaluate for jugular venous distension and consider BNP testing 1

By following this systematic approach to diagnostic testing, the cause of sudden onset ascites with right upper quadrant pain can be efficiently determined, allowing for appropriate management to reduce morbidity and mortality.