They are mainly produced by the cells of the pancreas and the salivary glands.
Pancreatic amylase breaks down (hydrolyzes) the ingested starch, completing its digestion in the first part of the small intestine (duodenum).
Under normal conditions, only small concentrations of amylase are found in the blood and urine. However, if there is damage to the pancreatic cells, the amount of enzymes released into the circulation is higher. For these reasons, an increase in the blood and urinary concentration of amylase can be indicative of a state of inflammation and other diseases affecting the pancreas.
The amylase test evaluates its presence and quantity in the blood and / or urine (the latter being the route of excretion). These enzymes are found in higher concentrations just when there is damage to the cells of the pancreas (for example, as a result of acute pancreatitis or a recurrence of chronic inflammation) or a "blockage of the pancreatic duct.
Amylase in the Blood
The concentration of amylase in the blood is called amylasemia and is determined on a simple venous blood sample; we speak of hyperamylasemia when this concentration is too high and hypoamylasemia when this concentration is lower than normal.
Amylase in the Urine
Since circulating amylases - by virtue of their low molecular weight - are eliminated, at least in part, in the urine, their concentration in serum also depends on renal function.
The concentration of amylase in the urine is called amylasuria (hyperamylasuria when it is too high, hypoamylasuria when it is below normal).
In some cases, for example when fluid builds up in the abdominal cavity (ascites), the amylase test may be performed on peritoneal fluid to help diagnose pancreatitis.
When is the exam prescribed?
The amylase test is not a routine test. This test is prescribed by the doctor when the patient has symptoms that lead to suspicion of an alteration in the pancreas.
Generally, symptoms that indicate the presence of pancreatic disease include:
- Severe abdominal pain;
- Fever;
- Lack of appetite;
- Weight loss with no apparent cause;
- Bad digestion
- Abdominal swelling
- Meteorism;
- Nausea.
Amylase testing may also be ordered when chronic hepatitis has been found or after removal of stones that have caused biliary colic.
Sometimes, amylasuria is prescribed with the determination of creatinine clearance, to evaluate the ratio of amylase to creatinine filtered by the kidneys. amylase).
Normal amylase values are on average:
- Amylase in serum: 1-225 international units per liter (I.U./l);
- Pancreatic fraction: 17-115 U.I./l;
- Salivary fraction: 17-135 U.I./l;
- Amylasuria: 25-1.500 I.U./24 hours.
Amylase and Pancreatitis
As mentioned, serum and urinary amylases represent important laboratory data, which help to diagnose acute and chronic pancreatitis. Increases in circulating amylases can also occur in cases of renal insufficiency and gynecological or small intestine pathologies.
PANCREATITIS (inflammation of the pancreas) is accompanied by symptoms such as severe abdominal pain, fever, loss of appetite or nausea; in chronic forms steatorrhea is typical.
During acute pancreatitis amylase often increases up to 4-6 times beyond the maximum values of the normal range. This increase occurs within 12 hours of the event and plasma amylases generally remain elevated for three to four days, while plasma amylases remain elevated for three to four days. amylasuria can remain high for up to 10 days. Chronic pancreatitis is often associated with alcoholism, but can also be caused by trauma, obstruction of the pancreatic duct and various genetic diseases, such as cystic fibrosis. In the presence of chronic pancreatitis, the amylase values in the blood can be moderately elevated or even normal and often decrease as the disease progresses due to poor organ function.
Other Causes of High Amylase
By virtue of the numerous conditions it accompanies, "hyperamylasemia - despite having a" high diagnostic sensitivity for acute pancreatitis - has a low specificity.
For this reason, it is often necessary to integrate it into the general clinical picture and into the results of other investigations. Apart from pancreatitis, blood amylase has however a poor diagnostic value, in the sense that the diseases and conditions that can alter its values are diagnosed without the need to control the amylasemia.
Another typical condition that leads to an increase in amylase in serum is the so-called macroamylase, in which these enzymes complex with globulins (proteins) of the blood, forming molecular aggregates that cannot be filtered and which are therefore not found in the urine. . In the presence of macroamylase, the serum dosage of lipases can provide useful information on a possible involvement of the pancreas.
Like amylases, lipases are also measurable and, since they are not produced by the salivary glands, they are a more specific index of pancreatic damage; furthermore, after the initial stages of the pancreatic inflammatory process, lipasemia tends to decrease less rapidly than amylasemia. However, the measurement of blood lipase is more difficult and it is for this reason that it is often preferred to evaluate serum amylase levels.
Laboratory investigations also make it possible to distinguish pancreatic isoforms from salivary ones, thus increasing the sensitivity and diagnostic specificity with respect to the total amylase assay.
The concentrations of amylase in the blood and urine may be moderately elevated in some conditions, such as: ovarian neoplasm, lung cancer, tubal pregnancy, acute appendicitis, diabetic ketoacidosis, mumps, intestinal obstruction or perforated ulcer.
However, amylase testing is not usually prescribed for the diagnosis and monitoring of these conditions.
Reduced blood and urinary amylase concentrations may also be indicative of permanent damage to pancreatic-producing cells. A low value may also be due to renal dysfunction or toxaemia gravidarum.
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