What lab tests should be done in an acute episode of acute pancreatitis to identify the cause and assess disease severity?

Laboratory and Diagnostic Testing in Acute Pancreatitis

Initial Laboratory Panel at Admission

All patients presenting with acute pancreatitis should have the following serum tests obtained immediately at admission: amylase or lipase, triglycerides, calcium, and liver chemistries (bilirubin, AST, ALT, alkaline phosphatase). 1

Diagnostic Confirmation

• Serum lipase is the preferred diagnostic test over amylase, with a diagnostic threshold of ≥3 times the upper limit of normal, offering superior sensitivity (79-89%) and specificity (89-94%) 2
• Lipase remains elevated for 8-14 days compared to amylase's shorter window, making it more reliable for delayed presentations 2
• Ordering both lipase and amylase together provides no diagnostic advantage 2

Etiological Determination

Liver Function Tests:

• Elevated AST, ALT, bilirubin, or alkaline phosphatase at admission strongly suggests gallstone etiology 1
• Early aminotransferase elevation is particularly predictive of biliary pancreatitis 1

Triglyceride Measurement:

• Critical to measure at admission because levels drop rapidly with fasting and IV fluids 3
• Triglyceride levels ≥1000 mg/dL definitively indicate hypertriglyceridemia-induced pancreatitis 3, 4
• Levels between 500-1000 mg/dL with lactescent serum should raise high suspicion, especially without other clear etiology 4
• If initial triglycerides are <1000 mg/dL but suspicion remains, measure fasting triglycerides after recovery 1

Calcium Level:

• Measure at admission to identify hypercalcemia as a potential cause 1, 2
• Hypercalcemia is less common but important not to miss 3

Severity Assessment Laboratory Tests

C-Reactive Protein (CRP):

• CRP ≥150 mg/L at 48-72 hours after symptom onset is the preferred laboratory marker for predicting severe disease 1, 5
• Sensitivity 38-61%, specificity 89-90% 5
• Major limitation: cannot be used for immediate severity assessment at presentation as peak levels only occur at 48-72 hours 5

Additional Severity Markers:

• Complete blood count for hematocrit and white blood cell count 2
• BUN and creatinine for renal function assessment 5
• Glucose and electrolytes for metabolic abnormalities 1

Clinical Scoring Systems:

• APACHE II score should be calculated, with a cutoff of >8 indicating predicted severe disease requiring intensive monitoring 1
• Multiple factor scoring systems are preferred over single laboratory values 1

Imaging Studies

Abdominal Ultrasonography:

• Should be obtained at admission in all patients to evaluate for cholelithiasis or choledocholithiasis 1
• If initial ultrasound is inadequate or gallstone suspicion persists, repeat after recovery 1
• Endoscopic ultrasound (EUS) can serve as an accurate alternative for screening gallstones 1

Contrast-Enhanced CT Scanning:

• Perform after 72 hours of illness in patients with predicted severe disease (APACHE II >8) or evidence of organ failure to assess pancreatic necrosis 1
• Use selectively based on clinical features in patients not meeting these criteria 1
• Not routinely needed in mild predicted cases unless clinical deterioration occurs 1

Special Circumstances

Unexplained Pancreatitis in Patients >40 Years:

• CT or EUS should be performed to exclude underlying pancreatic malignancy 1

Recurrent Pancreatitis:

• Consider EUS and/or ERCP, with EUS preferred as initial test 1
• ERCP should only be performed by experienced endoscopists with therapeutic capabilities 1

Autoimmune Pancreatitis Suspicion:

• Serum IgG4 level should be ordered, with >280 mg/dL being diagnostic for type 1 autoimmune pancreatitis 2

Common Pitfalls to Avoid

• Do not delay triglyceride measurement - levels normalize rapidly with treatment, potentially missing hypertriglyceridemia as the etiology 3
• Do not order routine CT at admission - wait 72 hours unless diagnostic uncertainty exists, as early CT underestimates necrosis 1
• Do not rely solely on CRP at admission - it requires 48-72 hours to reach diagnostic levels for severity prediction 5
• The etiology should be established in at least 75-80% of cases; more than 20-25% classified as "idiopathic" suggests inadequate workup 1