Initial Diagnostic Tests for Suspected Pancreatitis
Serum lipase is the preferred first-line laboratory test for suspected acute pancreatitis, with a diagnostic threshold of ≥3 times the upper limit of normal, and should be obtained at admission along with abdominal ultrasound. 1, 2, 3
Laboratory Testing
Primary Enzyme Testing
Serum lipase should be measured at admission as it demonstrates superior sensitivity (91%) compared to amylase (62%) and remains elevated longer (8-14 days versus 3-7 days for amylase). 2, 3
The diagnostic cutoff is ≥3 times the upper limit of normal for both lipase and amylase, which provides optimal balance between sensitivity and specificity. 2, 4
Lipase rises within 4-8 hours of pancreatic injury, peaks at 24 hours, providing an earlier and more reliable diagnostic window than amylase. 2
Amylase has poor specificity (only 71%) because salivary amylase elevations account for 90% of discordant cases where amylase is elevated but lipase is normal. 5
Additional Laboratory Tests at Admission
All patients should have the following measured at admission: 1
- Serum triglycerides - levels >1000 mg/dL definitively indicate hypertriglyceridemia-induced pancreatitis 6
- Serum calcium - to identify hypercalcemia as a potential cause 1
- Liver chemistries (bilirubin, AST, ALT, alkaline phosphatase) - to assess for biliary etiology 1
Imaging Studies
Initial Imaging
Abdominal ultrasound should be performed at admission in all patients to detect gallstones, biliary duct dilation, and free peritoneal fluid. 1, 2
Chest and abdominal plain radiographs should be obtained to provide baseline assessment and exclude other pathology such as perforated viscus or intestinal obstruction. 1
Advanced Imaging
Contrast-enhanced CT scan should be performed after 72 hours of illness onset in patients with predicted severe disease (APACHE II score >8) or evidence of organ failure during the initial 72 hours. 1, 2
CT performed before 72 hours may underestimate the amount of pancreatic necrosis and should be avoided unless clinical and biochemical findings are inconclusive. 1, 2
CT is occasionally indicated for diagnostic purposes when clinical and biochemical findings are inconclusive. 1
Severity Assessment
APACHE II scoring system is preferred for severity stratification, using a cutoff of 8. 1, 2
C-reactive protein >150 mg/L at 48 hours after disease onset can be used as an adjunct to clinical judgment and scoring systems. 1, 2
Clinical assessment alone is unreliable and will misclassify approximately 50% of patients. 2
Common Pitfalls to Avoid
Do not rely on amylase alone - it has poor sensitivity for alcoholic pancreatitis (the most common cause in urban hospitals) and can be elevated in numerous non-pancreatic conditions including renal disease, appendicitis, and bowel obstruction. 2, 7
Measure triglycerides early - levels can decrease rapidly with fasting and IV fluid administration, potentially missing hypertriglyceridemia as the etiology. 6
Do not use enzyme levels to monitor disease progression or guide treatment decisions - serial lipase measurements are not consistently accurate for predicting severity, and clinical assessment with imaging studies is more reliable. 2
The degree of enzyme elevation does not correlate with disease severity - patients can have severe pancreatitis with modest enzyme elevations. 2
Diagnostic Timeline
The correct diagnosis should be established within 48 hours of admission to avoid missing alternative life-threatening intra-abdominal catastrophes. 1