What labs should be checked to assess pancreatic function?

Pancreatic Laboratory Assessment

For assessing pancreatic function in chronic disease, serum enzyme testing is not recommended due to poor sensitivity, while fecal elastase or chymotrypsin are the preferred non-invasive tests; however, for acute pancreatitis diagnosis, serum lipase is the single best laboratory test.

Context-Dependent Approach

The laboratory workup for pancreatic assessment differs fundamentally based on whether you're evaluating acute pancreatitis versus chronic pancreatic insufficiency:

For Acute Pancreatitis Diagnosis

Serum lipase is the preferred first-line test, with a diagnostic cutoff of ≥3 times the upper limit of normal providing optimal accuracy 1. This recommendation comes from the American College of Gastroenterology and reflects lipase's superior performance characteristics 1.

Key advantages of lipase over amylase:

• Higher sensitivity (90-100% vs. 76-95%) 2, 3
• Longer diagnostic window, remaining elevated for days after symptom onset 4, 5
• Better performance in alcoholic pancreatitis and delayed presentations 4
• Only 2.9% of acute pancreatitis cases have normal lipase on initial testing, compared to 18.8% with normal amylase 2

Serum amylase can be used as an alternative but has important limitations 1:

• Less specific than lipase 4
• Shorter diagnostic window 5
• May be normal in hyperlipidemic pancreatitis, chronic pancreatitis exacerbations, and delayed presentations 4
• Use the same cutoff: ≥3 times upper limit of normal 1, 6

Co-ordering both lipase and amylase provides minimal additional diagnostic value and should be discouraged to reduce unnecessary costs 5, 3.

Additional Labs for Acute Pancreatitis Workup

Once acute pancreatitis is confirmed, obtain these tests for etiology determination and severity assessment 1:

Etiology workup:

• Liver function tests (bilirubin, AST, ALT, alkaline phosphatase) to evaluate biliary etiology 1
• Serum triglycerides if >1000 mg/dL (>11.3 mmol/L) indicates hypertriglyceridemia-induced pancreatitis 1
• Serum calcium to evaluate hypercalcemia as a cause 1

Severity assessment:

• C-reactive protein (CRP) at 48-72 hours: ≥150 mg/L predicts severe disease 1, 4
• Hematocrit: >44% is an independent risk factor for pancreatic necrosis 1
• Blood urea nitrogen (BUN): >20 mg/dL predicts mortality 1
• Procalcitonin: most sensitive for detecting pancreatic infection; low values strongly exclude infected necrosis 1

Important caveat: Daily enzyme measurements after diagnosis have no value in monitoring clinical progress and should be avoided 4.

For Chronic Pancreatic Insufficiency

Serum enzyme testing (lipase, amylase, trypsin) is NOT recommended for diagnosing chronic pancreatitis or pancreatic insufficiency 7. Here's why:

• Pancreatic disease must be extremely advanced (>90% acinar tissue destruction) before serum enzymes become significantly reduced 7
• Even in confirmed pancreatic insufficiency, only 50% of patients have abnormally low serum enzymes 7
• Many patients with marked functional impairment on invasive testing have normal serum enzyme levels 7
• Trypsin is the most useful of the three serum tests if you must check them, but sensitivity remains poor 7

Fecal tests are the preferred non-invasive approach for chronic pancreatic insufficiency 7:

• Fecal elastase - measured in stool samples 7
• Fecal chymotrypsin - good discriminatory capacity for normal versus severely impaired function 7
• Fecal lipase - also available but less commonly used 7

Key limitation: Fecal chymotrypsin alone is sufficient for patients with clearly normal or severely impaired function, but those with intermediate values require confirmatory testing 7.

Common Pitfalls to Avoid

• Don't rely on serum enzymes for chronic pancreatitis diagnosis - they lack sensitivity until disease is far advanced 7
• Don't order both lipase and amylase routinely - this increases costs without improving diagnostic accuracy 5, 3
• Don't repeat pancreatic enzymes daily in acute pancreatitis - they don't correlate with clinical progress 4
• Don't use enzyme levels alone to determine severity - use CRP, hematocrit, and BUN instead 1, 4
• Remember amylase can be normal in hyperlipidemic pancreatitis - always check triglycerides if clinical suspicion is high 4