Lipase is more sensitive and specific and stays raised longer
Expansion
Diagnostic threshold: an amylase or lipase over three times the upper limit of normal, with compatible pain, diagnoses acute pancreatitis without imaging.
| Amylase | Lipase | |
|---|---|---|
| Rises | 6 to 12 hours | 4 to 8 hours |
| Peaks | 24 hours | 24 hours |
| Normalises | 3 to 5 days | 8 to 14 days |
| Sensitivity and specificity | Lower | Higher |
Because amylase falls quickly, a late presentation can have a normal amylase with a clearly raised lipase, which is the main practical reason lipase is preferred.
Other causes of a raised amylase
- Abdominal: perforated peptic ulcer, mesenteric ischaemia, bowel obstruction, ruptured ectopic pregnancy, cholecystitis, ruptured aortic aneurysm
- Salivary: mumps, parotitis, salivary calculi, alcohol, and anorexia and bulimia
- Renal failure, since amylase is renally cleared
- Macroamylasaemia, a benign complex with immunoglobulin that cannot be filtered, giving a persistently raised amylase with a normal lipase and a low urinary amylase
- Diabetic ketoacidosis, head injury, some drugs
Falsely normal amylase in true pancreatitis: late presentation, hypertriglyceridaemia (which interferes with the assay), and acute-on-chronic pancreatitis where too little functioning tissue remains.
Severity is scored, not measured by the enzyme. The Glasgow-Imrie, Ranson and APACHE II scores, plus C reactive protein at 48 hours, guide management, and the commonest causes remain gallstones and alcohol.