Amilazalar

Clinical Significance
Amylase is primarily used in diagnosing pancreatic diseases. Amylase is a commonly measured enzyme due to the availability of inexpensive, easily automated methods. Although amylase is a sensitive indicator of acute pancreatitis, it is not specific as it can be elevated in several conditions unrelated to the pancreas.[49] Pancreatitis can be defined by two out of the three following criteria: abdominal pain, serum amylase and/or lipase levels more than three times the upper limit of normal, and abdominal imaging supporting characteristic findings of pancreatitis. Therefore, its clinical significance has been questioned.[50] In cases of elevated levels of amylase with little support for pancreatitis, alternative causes of hyperamylasaemia should be considered. [51]
Amylase is not useful in predicting the severity of an acute pancreatic episode or monitoring the condition. The magnitude of the increase in serum enzyme activity is not related to the severity of pancreatic involvement; however, the greater the rise, the greater the probability of acute pancreatitis. The lack of specificity of total amylase measurement has led to an interest in the direct measurement of P-type amylase instead of total enzyme activity for the differential diagnosis of patients with acute abdominal pain.[19] By applying the best decision limit (an activity equal to threefold the URL), the specificity of P-type amylase for diagnosing acute pancreatitis is greater than 90%. Sensitivity in late detection of this condition is also notably improved with P-AMY. P-type amylase values remain increased in 80% of patients with uncomplicated pancreatitis one week after onset when only 30% still show increased total amylase activity.[52] This long-standing increase in P-type amylase activity in serum also makes redundant the traditional measurement of total amylase in urine—a test performed to achieve better diagnostic sensitivity in the late phase of pancreatitis.[53]
Amylase inhibitors such as acarbose have been used in treating type 2 diabetes and have been shown to reduce hemoglobin A1C and peak postprandial glucose. Acarbose has also been shown to improve the remission of dumping syndrome in bariatric patients. The drug has also been shown to improve the risk of cardiovascular disease by slowing down the thickening of carotid arteries.[54] Elevated amylase can be seen in a wide variety of conditions. It is important for clinicians to have a clear, stepwise approach when hyperamylasemia is found. This will help avoid unnecessary hospitalization and delayed or inappropriate treatment.[55] Biliary tract diseases, such as cholecystitis, cause up to a fourfold increase in serum P-type amylase activity due to primary or secondary pancreatic involvement.[56]
Various intra-abdominal events can lead to a significant increase in serum P-type amylase activities, up to a fourfold increase and sometimes beyond. Such increases may be caused by leakage of P-type amylase from the intestine into the peritoneal cavity and then into circulation.[57] In renal insufficiency, serum amylase activity is increased in proportion to the extent of renal impairment (usually, no more than five times the URL).[58]
Cases of amylase-producing multiple myeloma have been described. Increased amylase activity is due to salivary-type hyperamylasemia in most patients (sialyl salivary type).[59] A common feature of the myeloma cell lines associated with hyperamylasemia is a translocation of chromosome 1, which harbors the gene for amylase. The link does not appear to be immunoglobulin class-specific. The onset of hyperamylasemia is reported to be associated with a rapid disease progression, extensive bone destruction, and increased mortality, hence serum amylase activity may be a useful prognostic ‘tumor marker’ (the activity decreases in response to treatment and increases at times of relapse) in patients with multiple myeloma.[60][61] The amylase isoenzyme in cases of ruptured ectopic pregnancy is not well characterized. In severe cases presenting late, the increased isoenzyme may be P-AMY (from pancreatic involvement related to peritonitis), even though S-AMY is present in the fallopian tube.[62]
Some patients with phaeochromocytoma/paraganglioma were found to have hyperamylasemia, usually the salivary isotype. Here, hyperamylasemia may be related to the hypertensive crisis and vasoconstriction leading to tissue hypoxia rather than being a result of tumor secretion and is often transient.[63] Salivary-type hyperamylasemia has also been observed in various conditions without salivary gland disorders, such as diabetic ketoacidosis, pneumonia, and postoperative states in a wide variety of surgical interventions, including extra abdominal procedures such as post-coronary bypass.[64]
Benign pancreatic hyperenzymemia, a syndrome first described by Gullo, is characterized by raised serum amylase, pancreatic isoamylase, lipase, and trypsin activities in asymptomatic subjects with no evidence of pancreatic disease by imaging. The syndrome occurs sporadically or in a familial form, and amylase activity fluctuates significantly with occasional transient normalization in some cases.[65] CFTR, SPINK1, and PRSS1 gene mutations do not seem to have a role in the etiology of the condition, and benign pancreatic hyperenzymemia cannot be explained by mutations in genes whose variants are known to be associated with pancreatitis or by mutations in other PRSS1/SPINK1 genes.[66] It was found that about one-third of patients with chronic nonpathological pancreatic hyperenzymemia had abnormally high fecal calprotectin concentrations and they recommended evaluating the finding for the possible link between intestinal ecology and pancreatic enzyme alteration.[67]
Damage of salivary glands, leading to salivary hyperamylasemia, has been seen in trauma or surgery to the salivary gland, radiation to the neck area involving the parotid gland and subsequently causing duct obstruction or calculi of the salivary glands.[14] Another cause of subclinical damage to the salivary gland is chronic alcoholism and anorexia nervosa. Salivary amylase activity is three times higher than normal in 10% of patients with alcoholism; this may also be related to chronic liver disease.[68]
Hyperamylasemia in anorexia nervosa is associated with vomiting, and indeed the finding of raised salivary amylase may provide a clue to concealed vomiting.[69] However, pancreatitis may occur in these patients, particularly during the course of refeeding and so measurement of plasma lipase and/or amylase isoenzymes may be justified to differentiate pancreatitis from salivary hyperamylasemia.[70]
Hyperamylasemia may be associated with various tumors caused by either an ectopic production of the enzyme by the tumors or perhaps an inflammatory response by the tumor cells resulting in the marked release of the enzyme normally produced in these tissues into the bloodstream.[71] The raised isoenzyme is almost exclusively salivary type in ovarian, lung cancer, multiple myeloma, and pheochromocytoma.[72] Amylase-producing tumors of the lung are rare and may comprise in total only 1 to 3% of all lung carcinomas, and in these cases, the salivary amylase isotype is generally found. Amylase-producing lung carcinomas are mostly adenocarcinomas, but hyperamylasemia has also been reported in small cell carcinoma.[73] Amylase activity has been suggested as a useful tumor marker for monitoring the patient’s treatment in amylase-producing lung carcinoma.[74] One study reported that 39% of patients with ovarian carcinoma had hyperamylasaemia, which is salivary-type dominant, and that salivary amylase may be useful in the evaluation of radiotherapy effectiveness in this context.[75]
Gut diseases, including mucosal inflammatory disease of the small intestine, mesenteric infarction, intestinal obstruction, appendicitis, and peritonitis, usually result in increased P-type isoamylase because of increased absorption of amylase from the intestinal lumen.[76] Gut perforation is associated with leakage of intestinal contents into the peritoneum, causing inflammation and absorption of amylase across the inflamed peritoneum. This can result in hyperamylasemia. Acidosis, which can be due to (1) ketoacidosis that results in increased S-type and P-type isoamylases or (2) nonketotic acidosis that results in increased S-type isoamylase, can cause hyperamylasemia.[77] Amylase increases may occur postoperatively, resulting in increased S-type and P-type isoamylases; however, an increase in salivary amylase is more common.[78] This may occur after extracorporeal circulation or nonabdominal surgery (e.g., 30% of patients undergoing cardiac surgery have elevated S-type isoamylase).[79]
Rare cases of hyperamylasemia have been reported in association with systemic lupus erythematosus (SLE), as well as with ciprofloxacin treatment.[80] Other causes of hyperamylasemia include pneumonia (increased salivary amylase), cerebral trauma, burns, abdominal aortic aneurysms (increased pancreatic amylase), drugs (increased salivary and/or pancreatic amylase), anorexia nervosa and bulimia (increased salivary amylase), non-pathologic (increased salivary and/or pancreatic amylase), and organophosphate poisoning. Postprocedure balloon-assisted enteroscopy has also been associated with elevated amylase levels; measure pancreatic amylase levels rather than total amylase levels following these procedures.[3][81] Elevated pancreatic enzymes can be found in critically injured trauma patients, even in the absence of true pancreatitis.[82] 
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