What labs should be checked to diagnose acute pancreatitis?

Laboratory Tests for Diagnosing Acute Pancreatitis

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

Primary Diagnostic Tests

Essential Laboratory Tests

• Serum lipase:

  • First-line test with superior sensitivity (91%) and specificity (92%) 2
  • Remains elevated longer (8-14 days) than amylase, providing a wider diagnostic window 3
  • Rises within 4-8 hours of onset and peaks at 24 hours 3
  • Diagnostic threshold: ≥3 times upper limit of normal 3, 1

• Serum amylase:

  • Less sensitive than lipase, particularly in alcohol-induced pancreatitis 1
  • Rises within 6-24 hours, peaks at 48 hours, normalizes within 3-7 days 3
  • Diagnostic threshold: ≥3 times upper limit of normal 3
  • Not recommended as sole test if lipase is available 1, 4

Additional Initial Laboratory Tests

When acute pancreatitis is suspected, also check:

• Complete blood count (CBC)
• Liver function tests (bilirubin, AST, ALT, alkaline phosphatase) 3
• Triglyceride levels 3
• Calcium levels 3
• Blood urea nitrogen (BUN) and creatinine

Prognostic Laboratory Markers

For severity assessment and prognosis:

• C-reactive protein (CRP):

  • ≥150 mg/L at 48-72 hours is a prognostic factor for severe acute pancreatitis 3, 1
  • More valuable for severity assessment than enzyme levels 1

• Hematocrit: >44% represents an independent risk factor for pancreatic necrosis 3, 1

• Blood urea nitrogen: >20 mg/dL is an independent predictor of mortality 3, 1

• Procalcitonin: Most sensitive laboratory test for detecting pancreatic infection; low values strongly predict absence of infected necrosis 3

Diagnostic Algorithm

1. Initial presentation with abdominal pain:

   • Order serum lipase (preferred) or amylase if lipase unavailable
   • Order CBC, liver function tests, triglycerides, calcium, BUN/creatinine

2. Interpretation:

   • Lipase or amylase ≥3 times upper limit of normal + compatible clinical symptoms = diagnostic of acute pancreatitis
   • Levels <3 times upper limit are consistent with but not diagnostic of pancreatitis 3, 1

3. If diagnosis remains uncertain:

   • Consider contrast-enhanced CT scan 3
   • Note: Early CT (within 72 hours) may underestimate pancreatic necrosis 3

4. For etiology determination:

   • If no obvious gallstones or alcohol history, check:
     • Triglycerides (>1000 mg/dL indicates hypertriglyceridemic pancreatitis) 3, 1
     • Calcium levels (hypercalcemia can cause pancreatitis) 3
     • Consider abdominal ultrasound to assess for gallstones 3

Important Clinical Considerations

• Co-ordering both lipase and amylase provides minimal additional diagnostic benefit and increases costs unnecessarily 1, 4

• Enzyme levels alone cannot determine severity of pancreatitis; use clinical assessment, APACHE II scores, and other markers like CRP 3, 1

• Normal amylase does not rule out pancreatitis, especially in late presentations (>3 days) when amylase may have normalized 1

• Timing matters: Diagnostic accuracy of both enzymes decreases significantly after 3-5 days from symptom onset 5

By following this evidence-based approach to laboratory testing, clinicians can efficiently diagnose acute pancreatitis while minimizing unnecessary testing and costs.