What labs are used to diagnose pancreatitis?

Diagnostic Laboratory Tests for Pancreatitis

Serum lipase is the preferred laboratory test for diagnosing acute pancreatitis, with a cutoff value of three times the upper limit of normal providing optimal diagnostic accuracy. 1

Primary Diagnostic Tests

• Serum lipase is the gold standard laboratory test for diagnosing acute pancreatitis, offering higher sensitivity and specificity than amylase 1, 2
• Serum amylase can be used but is less specific and has a shorter diagnostic window than lipase 1
• The cutoff value for diagnosis is typically:
  • Lipase: greater than three times the upper limit of normal 1
  • Amylase: greater than three times the upper limit of normal 1, 3

Advantages of Lipase over Amylase

• Lipase remains elevated longer (4-8 hours onset, peaks at 24 hours, remains elevated for 8-14 days), providing a larger diagnostic window 1
• Higher specificity as there are fewer non-pancreatic sources of lipase 1, 2
• More sensitive than amylase (79% vs 72%) according to Cochrane review 1
• Several evidence-based guidelines recommend using lipase over amylase 2

Additional Laboratory Tests for Etiology and Severity Assessment

After confirming the diagnosis with lipase/amylase, these additional tests help determine etiology and severity:

• Liver function tests (bilirubin, AST, ALT, alkaline phosphatase) - to evaluate for biliary etiology 1
• Serum triglycerides - levels >11.3 mmol/L (>1000 mg/dL) indicate hypertriglyceridemia-induced pancreatitis 1
• Serum calcium - to evaluate for hypercalcemia as a potential cause 1
• C-reactive protein (CRP) - levels ≥150 mg/L at 48-72 hours can predict severe acute pancreatitis 1
• Hematocrit >44% - represents an independent risk factor for pancreatic necrosis 1
• Blood urea nitrogen >20 mg/dL - independent predictor of mortality 1
• Procalcitonin - most sensitive test for detecting pancreatic infection; low values are strong negative predictors of infected necrosis 1

Common Pitfalls and Caveats

• Neither lipase nor amylase alone can determine the severity or etiology of acute pancreatitis 2, 4
• Co-ordering both lipase and amylase provides minimal additional diagnostic value and increases costs unnecessarily 2, 5
• Non-pancreatic conditions can cause elevated lipase and amylase (renal disease, appendicitis, cholecystitis, intestinal obstruction) 1, 4
• Serum enzyme levels may be normal in late presentations of pancreatitis (>3-5 days after symptom onset) 6, 3
• Using cutoff values less than three times the upper limit of normal results in poor specificity 1, 3

Diagnostic Algorithm

1. Initial laboratory evaluation:

   • Serum lipase (preferred) or amylase 1
   • Complete blood count with hematocrit 1
   • Comprehensive metabolic panel including BUN, calcium 1
   • Liver function tests 1

2. If lipase/amylase >3x upper limit of normal:

   • Diagnosis of acute pancreatitis is confirmed 1
   • Proceed to etiology workup (triglycerides, calcium, liver function) 1
   • Assess for severity (CRP at 48-72h, hematocrit, BUN) 1

3. If lipase/amylase <3x upper limit of normal but clinical suspicion remains high:

   • Consider imaging (ultrasound, CT) to confirm diagnosis 1
   • Consider alternative diagnoses 4, 3

4. For monitoring disease progression:

   • Serial CRP measurements (peak at 48-72 hours) 1
   • Serial hematocrit and BUN measurements 1
   • Procalcitonin if infection is suspected 1