What is pancreatitis and what is the normal amylase range?

Pancreatitis and Amylase Range

Acute pancreatitis is an inflammatory disease of the pancreas characterized by acute inflammation and acinar cell destruction, diagnosed when at least two of three criteria are present: abdominal pain consistent with the disease, biochemical evidence of pancreatitis (serum amylase and/or lipase greater than three times upper limit of normal), and characteristic findings on abdominal imaging. 1, 2

Definition and Diagnosis of Pancreatitis

• Acute pancreatitis presents with upper abdominal pain and vomiting with epigastric or diffuse abdominal tenderness 1, 2
• Diagnosis requires at least two of three criteria: compatible abdominal pain, elevated pancreatic enzymes, and characteristic imaging findings 1
• Most patients (80-85%) develop mild disease (self-limited, mortality <1-3%), but approximately 20% will have moderate or severe disease with mortality rates of 13-35% 1
• Severe acute pancreatitis is associated with persistent organ failure (cardiovascular, respiratory, and/or renal) and high mortality 1

Amylase and Lipase in Diagnosis

• Serum amylase activity ≥4 times above normal or lipase activity ≥2 times the upper limit of normal is diagnostic in the appropriate clinical setting 1, 2
• Lipase is preferred over amylase due to higher specificity, longer elevation period (8-14 days vs 3-7 days for amylase), and higher sensitivity 3, 2
• The American Gastroenterological Association recommends determining if amylase elevation is significant (>3 times upper limit of normal), which is most consistent with acute pancreatitis 3
• Serum amylase may be normal in up to one-fifth of patients with acute pancreatitis; therefore, this level by itself is not a reliable diagnostic factor 4
• The severity of acute pancreatitis is independent of the elevation in serum amylase/lipase level (≤3n or >3n) on admission 5

Normal Amylase Range and Interpretation

• Normal serum amylase range varies by laboratory but is typically 30-110 U/L 3
• Amylase rises within 6-24 hours of pancreatic injury and normalizes in 3-7 days 3
• Amylase levels ≥3 times the upper limit of normal have improved diagnostic specificity 3, 6
• At appropriately selected cutoff levels (3-4 times upper limit of normal), amylase can be effectively used as the first-line test with sensitivity of 84-92% and specificity of 98% 6

Important Caveats About Amylase Levels

• Patients with only a slight increase in amylase/lipase can still have or develop severe acute pancreatitis 5
• Diagnostic amylase levels are significantly lower in alcoholic pancreatitis compared to gallstone pancreatitis 7
• Elevated amylase can occur in non-pancreatic conditions including head injuries, hepatic injuries, bowel injuries, renal disease, appendicitis, acute cholecystitis, and bowel obstruction 3
• Persistently elevated serum amylase after 10 days from initial injury should be monitored closely due to increased risk of pseudocyst formation 3

Management Based on Severity

• Treatment approach should be based on severity classification (mild, moderately severe, or severe) 2
• Patients with organ failures should be admitted to an intensive care unit whenever possible 1
• Patients who have persistent organ failure with infected necrosis have the highest risk of death 1
• Early aggressive fluid rehydration with lactated Ringer solution and close monitoring within the first 12 to 24 hours may decrease risk of progression to systemic inflammatory response syndrome 4

Imaging in Pancreatitis

• Ultrasound examination should be performed initially in all patients with suspected acute pancreatitis to detect gallstones, free peritoneal fluid, and bile duct dilation 3, 2
• CT scan with IV contrast is indicated when clinical and biochemical findings are inconclusive or severe disease is predicted 3, 2
• CT scan should be performed after 72 hours of illness onset to avoid underestimating pancreatic necrosis 3