Causes of increased and decreased amylase

In acute pancreatitis, blood and urine amylase increases 10-30 times. Hyperamylasemia occurs at the onset of the disease (after 4-6 hours), reaches a maximum after 12-24 hours, then quickly decreases and returns to normal on the 2nd-6th day. The level of increase in serum amylase activity does not correlate with the severity of pancreatitis.

Amylase activity in urine begins to increase 6-10 hours after an acute attack of pancreatitis and returns to normal after 3 days. In some cases, amylase activity in urine has two waves of increase within 3 days. The diagnostic sensitivity of determining amylase in blood serum for acute pancreatitis is 95%, specificity is 88%.

Acute pancreatitis may occur without an increase in amylase activity (in particular, with pancreatic necrosis). In the first 24 hours from the onset of the disease, normal levels of urine amylase activity are detected in 25% of patients with abortive pancreatitis, 20% with fatty pancreatitis, and 10% with hemorrhagic pancreatitis. More accurate information is obtained by studying the amylase activity in the daily volume of urine. An important, and in some cases decisive, significance for recognizing the recurrent form of acute pancreatitis is a repeated increase in the activity of blood and urine amylase during repeated relapses of the pain syndrome. With different forms of acute pancreatitis, the dynamics of the increase in alpha amylase in the blood and urine is different. Thus, short-term amylasemia on the 1st-3rd day of the disease is characteristic of edematous pancreatitis; for fatty pancreatic necrosis - high and prolonged amylaseemia, and for hemorrhagic pancreatic necrosis - short-term hyperamylaseemia on the 3rd day of the disease. Pathogenetically, hyperamylase develops as a result of blockade of the excretory ducts of the pancreas by edematous interstitial tissue and is most characteristic of fatty pancreatic necrosis. In hemorrhagic pancreatic necrosis, a sharp increase in the activity of α-amylase in the blood is noted, followed by a rapid decrease, which reflects the progression of necrosis.

Hyperamylasemia and hyperamylasuria are important but not specific signs of acute pancreatitis; in addition, an increase in their activity may be short-lived. To increase the informativeness of the obtained study results, it is useful to combine the determination of blood and urine amylase activity with a parallel determination of the concentration of creatinine in urine and blood serum. Based on these data, the amylase-creatinine clearance index is calculated using the following formula:

[(AM×KrS)/(KrM×AC)]×100,

Where AM is urine amylase; AC is serum amylase; KrM is urine creatinine; KrS is serum creatinine.

Normally, the amylase-creatinine index is no more than 3, its increase is considered a sign of pancreatitis, since in pancreatitis the level of true pancreatic amylase increases, and its clearance is 80% faster than the clearance of salivary amylase. However, it has been established that in acute pancreatitis, the clearance of both beta- and S-amylase increases significantly, which is explained as follows. In healthy people, serum amylase is initially filtered in the renal glomeruli and then reabsorbed by the tubular epithelium. In acute pancreatitis, the mechanism of tubular reabsorption is suppressed due to excessive excretion of beta- and S-amylase. Since the amylase activity of serum in acute pancreatitis is mainly due to beta-amylase, then with an increase in the clearance of total amylase, the clearance of beta-amylase increases. In acute pancreatitis, serum amylase activity and amylase-creatinine clearance are usually elevated due to suppression of the renal mechanism of tubular reabsorption of amylase. In diseases occurring under the guise of pancreatitis, serum amylase activity may increase, but the amylase-creatinine clearance remains normal, since there is no tubular defect. It is very important for this study to collect blood and urine at the same time.

In chronic pancreatitis, amylase activity in the blood and urine increases (in 10-88% and 21-70% of patients, respectively) during an exacerbation of the process and when there are obstacles to the outflow of pancreatic juice (inflammation, swelling of the head of the pancreas and compression of the ducts, cicatricial stenosis of the duodenal papilla, etc.). In the sclerotic form of pancreatitis, hyperamylasemia is also determined by the degree of obstruction of the ducts and the functional capacity of the remaining part of the gland. To increase the sensitivity of the study of amylase activity in the blood and urine in chronic pancreatitis, A.I. Khazanov (1997) recommends conducting their analysis on the first day of hospital stay, then at least twice after instrumental studies (fibrogastroduodenoscopy, X-ray examination of the stomach and intestines, etc.), as well as at the time of increased abdominal pain. In this case, the sensitivity of the test increases from 40 to 75-85%.

In chronic pancreatitis with fibrous changes in the pancreas, exacerbations, often pronounced and widespread, are accompanied by a relatively small increase in amylase activity.

Due to the impairment of the functional capacity of the pancreas, hyperamylasemia may often be absent in acute purulent pancreatitis (with extensive “total” necrosis of the pancreas).

In pancreatic cancer, amylase activity in the blood and urine may increase, but often remains within normal limits or even decreases.

Evaluation of the results of amylase activity tests in blood and urine is complicated by the fact that the enzyme is also found in the salivary glands, large intestine, skeletal muscles, kidneys, lungs, ovaries, fallopian tubes, and prostate gland. Therefore, amylase activity may be elevated in a number of diseases that have a picture similar to acute pancreatitis: acute appendicitis, peritonitis, perforated gastric ulcer and duodenal ulcer, intestinal obstruction, cholecystitis, mesenteric vascular thrombosis, as well as pheochromocytoma, diabetic acidosis, after heart defect surgeries, after liver resection, high alcohol intake, sulfonamides, morphine, thiazide diuretics, and oral contraceptives. Increased amylase activity in these diseases is due to a number of reasons and is reactive in most cases. Due to significant reserves of amylase in acinar cells, any disruption of their integrity or the slightest obstruction of pancreatic secretion outflow can lead to a significant amount of amylase entering the blood. In patients with peritonitis, an increase in amylase activity may reflect the proliferation of amylase-forming bacteria. Typically, alpha-amylase activity in the blood increases 3-5 times in the diseases listed above.

A decrease in alpha amylase activity in the blood is possible with thyrotoxicosis, myocardial infarction, and pancreatic necrosis.

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