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Lipases are a group of enzymes that hydrolyze the glycerol esters of long chain fatty acids. Serum lipase is mainly derived from the pancreatic acinar cells, where it is synthesized and stored in granules. Normally, more than 99% of stored enzyme is secreted into the pancreatic duct and less than 1% diffuses across cell membranes and reaches the circulation via lymphatics and capillaries. In acute pancreatitis, acinar cell membranes become more permeable, allowing much more enzyme to reach the circulation. In hemorrhagic pancreatitis, cellular necrosis leads to even more release of enzyme. Lipase is cleared from plasma by glomerular filtration and is subsequently almost totally reabsorbed and metabolized by the renal tubules. The circulating half-life of lipase is between 7 and 14 hours.

Serum lipase activity increases within 4 to 8 hours after the onset of acute pancreatitis, peaks at 24 hours and decreases within 8 to 14 days. Lipase levels usually increase from 7 to 11 times the upper limit of normal in acute pancreatitis. Rarely, will lipase stay increased more than 14 days. Prolonged increases signal poor prognosis or the presence of a pancreatic cyst. Initially, the rise in lipase is approximately equal to that of amylase, but after 24 hours lipase has greater clinical sensitivity. Lipase activity remains elevated longer than amylase. Some patients may have elevated lipase and normal amylase activity due to the greater concentration of lipase in the pancreas and its longer serum half-life.

Lipase may also be increased in chronic pancreatitis and pancreatic duct obstruction. Pancreatic duct obstruction by fibrous strictures, stones, tumors, or edema increases the secretory pressure and promotes extravasation of lipase into the pericapillary spaces. Lipase is not specific for pancreatic disease and may be increased in renal disease, acute cholecystitis, bowel obstruction, intestinal infarction, duodenal ulcers, liver disease, alcoholism, diabetic ketoacidosis, and after endoscopic retrograde cholangiopancreatography. Patients with renal failure may have lipase levels three times the upper limit of normal.

Hospitalized patients with nonpancreatic diseases may have lipase values at or slightly above the upper limit of normal, which was established with samples from healthy, nonhospitalized individuals.

Some individuals may have persistently elevated lipase and normal amylase activities. This combination of results should suggest the presence of macrolipase, which is an immune complex between lipase and IgG. Increased enzyme activity is due to the inability of the kidney to excrete the lipase complex.

Lipase reference range is 18 – 51 U/L on a Beckman Coulter DXc and 400 - 300 U/L on a Vitros analyzer.

Specimen requirement is one SST tube of blood.

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