Lipase hydrolyzes triglycerides. There are several forms of lipase: pancreatic lipase, colipase and lipoprotein lipase. Colipase is cleared by the kidney, and can result in increased lipase concentrations when there is a decreased GFR. Lipoprotein lipase is produced by vascular endothelium and is essential in triglyceride metabolism
These are based on hydrolysis of an olive oil emulsion into constituent fatty acids.
Causes of increased lipase
- Titrometric - This estimates the quantity of sodium hydroxide needed to neutralise fatty acids produced by lipase activity.
- Nephelometry - Triolein (long chain fatty acids) is degraded to diglycerides. The degradation of triolein results in decreased turbidity. Hemolysis and icterus can result in falsely low values.
- Colorimetric - This measures the rate of dye formation yielded from the breakdown of long chain fatty acids and is the current procedure used at Cornell. Severe lipemia may inactivate the enzyme.
- Drugs : Corticosteroids are reported to increase lipase values.
- Acute pancreatitis: Destruction of pancreatic acinar tissue results in the escape of
pancreatic enzymes into the pancreas and peritoneal cavity. The enzymes enter the
blood by way of lymphatics or capillaries with subsequent elevation of serum levels. Increases of at least 2 x normal are seen in pancreatitis. In dogs, lipase increases within 24 hours and peaks (at a higher level than amylase) at 2-5 days. Increases of 3 times normal support a diagnosis of pancreatitis more strongly
than more moderate increases, which may be accounted for by non-pancreatic causes. Lipase may be normal in up to 28% of dogs with pancreatitis.
In the cat, lipase is not consistently elevated in pancreatitis. It was hoped that measurement of trypsin-like immunoreactivity (TLI) would be better for diagnosis in cats, as high values are seen in dogs with pancreatitis and are very useful for diagnosis in dogs with normal lipase values. However, recent data suggests that TLI values are not consistently increased in cats with confirmed pancreatitis, limiting the usefulness of this test to cats with exocrine pancreatic insufficiency.
- Gastrointestinal disease: Peritonitis, gastritis, bowel obstruction, visceral manipulation (laparotomy), hepatic disease and neoplasia may increase lipase values by 2-3 x normal.
- Decreased GFR: Increases of up to 4 x normal may be seen in patients with decreased GFR. In azotemic patients with lipase levels greater than 3-4 times normal, the
diagnosis of pancreatitis should still be considered.