Lipases are enzymes that hydrolyze glycerol esters with long-chain fatty acids. Pancreatic lipase is a single-chain glycoprotein with a molecular weight of 48 kDa. The concentration of lipase in the pancreas is 5000-fold higher than in other tissues, and the concentration gradient between pancreas and serum is ∼20,000-fold. Most of the lipase activity in serum comes from pancreatic acinar cells, but a small amount is also secreted by gastric, pulmonary, and intestinal mucosa. Lipase is a molecule small enough to be freely filtered through the glomerulus. It is totally reabsorbed by the renal tubules and is therefore not detectable in the urine.
Clinical Significance
 Serum lipase measurement represents the recommended laboratory test for the diagnosis of acute pancreatitis. The clinical sensitivity is 80–100% depending on the selected decision level and the clinical specificity of 80–100% depending on the population to which the test is applied. After an attack of acute pancreatitis, serum lipase activity increases within 4–8 hours, peaks after ∼24 hours, and values return to basal levels within 7–14 days. Increases between 2 and 50 times the URL have been reported, but it is important to remember that the magnitude of the increase in lipase activity is not necessarily proportional to the severity of the attack.
Acute pancreatitis is sometimes difficult to diagnose because it must be differentiated from other serious intra- abdominal disorders with similar clinical findings, such as perforated gastric or duodenal ulcer or intestinal obstruction. In the differential diagnosis, increased serum lipase concentrations >3 times the URL, in the absence of renal insufficiency, is a more specific diagnostic finding than increased serum α-amylase activity. In addition, lipase concentrations remain increased longer than α-amylase concentrations, which is another advantage in patients with delayed clinical presentation. Therefore, it is recommended that lipase should replace α-amylase determination as to the first diagnostic step for acute pancreatitis in a clinical emergency; on the other hand, simultaneous measurement of both enzymes is not warranted.
In subjects with reduced glomerular filtration rate, serum lipase activity is increased. Therefore, caution should be paid in the interpretation of increased lipase values in the presence of renal disease.
Reference Intervals
Among the most clinically essential enzymes, lipase is the only one whose measurement (and consequently the result) is method dependent. The reference intervals of lipase are, therefore, method dependent. For methods based on the use of diglycerides as a substrate, the suggested URL is 45 U/L, whereas the method using methylresorufin as a substrate has an URL of 64 U/L. There are no differences related to gender or age