- 50 units
The enzyme lipase catalyzes the hydrolysis of triglycerides (triacylglycerols). Lipase is a glycoprotein with at least two known isoenzymes1. Lipase is very non-specific, catalyzing the breakdown of most triglycerides. The reaction shown below is just one example of such a reaction catalyzed by lipase. In this case the substrate is triolein, a triglyceride in which all three fatty acids are oleic acid, a common substrate used in lipase reagents. Lipase preferentially cleaves the fatty acids on the ends, leaving a beta-monoglyceride as shown below. This monoglyceride spontaneously (but slowly) rearranges to an alpha-triglyceride which can then be cleaved by lipase2. Thus eventually all three bonds will be cleaved by lipase resulting in three fatty acids and one molecule of free glycerol.
Lipase is somewhat unusual in that its common substrates (triglycerides) are not soluble in water and therefore must be emulsified in order to be hydrolyzed by lipase. This emulsification is performed in vivo by bile salts3. Lipase can only act on the surface of the dispersed substrate, and in addition requires a cofactor, colipase, which helps it attach to this surface4,5.
The main clinical utility of lipase along with amylase, is for the diagnosis of acute pancreatitis. Although both are usually measured, lipase is far superior to amylase6,7 as a marker for pancreatitis, reaching 95% sensitivity and specificity8. Lipase assay methods are extremely variable and may use emulsified triglycerides or water soluble analogs. Intra-assay variability is one of the main limitations of lipase’s clinical utility9. Nevertheless some have asked the question as to whether lipase should not replace amylase altogether, even with including amylase isoforms, for the diagnosis of acute pancreatitis10.
Other diagnostic applications of lipase have been occasionally reported including obstruction of the pancreatic duct and pancreatic cancer11, but in general, the main utility of lipase is limited to acute pancreatitis.
|ADULT REFERENCE RANGE2:||< 38 U/L|