What are amylases? The amylase are enzymes involved in the carbohydrate breakdown process.
They are distinguished in salivary amylase is pancreatic amylase.
The first, produced by the salivary glands, represents about 60% of the total, the second, typically pancreatic, represents about 40%.
Salivary amylase has a fleeting action, as it is prematurely inactivated by the acid pH of the stomach. Pancreatic amylase, on the other hand, produced in the pancreas together with other enzymes - also involved in the digestion of food - is poured into the duodenum (the first portion of the small intestine) especially during the post-prandial phase - that is, after eating .
Amylases allow the cleavage (hydrolysis) of alpha-1,4 glucosidic bonds (bonds typical of polysaccharides) and the products of hydrolysis by amylases are: dextrins, maltotriose is maltose.
The other enzymes produced in the pancreas are others diastasis, involved in the breakdown of sugars, the lipase, involved in the process of breaking down fats, e protease such as trypsin, chymotrypsin is carboxypeptidase involved in the hydrolysis process of proteins.
Normal amylase values
THE normal values of the amylases are:
- total amylase or total amylase: 26-102 U / L
- pancreatic amylase: 6-55 U / L
- amylasuria 24-408 IU 24h urine
Hyperamylasemia - High amylases
In pathological conditions, an increase in these values can occur. Let's see what are the main causes of high pancreatic amylase.
Causes of high amylase
The main causes of hyperamylasemia I'm:
- acute pancreatitis
- obstruction of the pancreatic duct (e.g. due to stones or pancreatic cancer)
- salivary gland infections
- obstruction of the salivary glands
- rupture of the esophagus (the enzyme in this case will be of salivary origin)
- kidney failure
- intestinal obstruction and / or perforation
- peptic ulcer
- aortic aneurysm
- ectopic pregnancy
Amylases, while also increasing in extra-pancreatic diseases, have a predominantly role in the diagnosis of pancreatitis.
Evaluation of urinary amylase dosage is recommended to rule out hyperamylaseemia associated with macroamylaseemia.
Macroamylasemia is a condition associated with the presence of immune complexes consisting of anti-amylase antibodies and amylase (predominantly salivary); due to their size, urinary elimination will not be possible and therefore there will be an increase in amylasemia, which however is often asymptomatic.
So how can we distinguish an increase in amylase associated with organic pathology or with macroamylasemia?
To distinguish the two conditions it is advisable to measure amylasuria - that is the presence of amylase in the urine - which, if reduced, is associated with a condition of macroamylasemia rather than with pancreatic damage.
What is pancreatitis? There pancreatitis it is an inflammation of the pancreas that is associated with a typical symptomatology: the so-called bar pain, upper abdominal pain, which may also extend to the back.
Concomitant symptoms can be: nausea, temperature, loss of appetite is weight loss.
Several aspects can help us in the evaluation of a condition associated with pancreatitis:
- in the early stages we will have a increased blood sugar, resulting from alterations in the pancreatic parenchyma and the release into the circulation of glucagon - hyperglycemic hormone produced by pancreatic alpha cells.
- in the subsequent stages, as the destruction of the pancreatic parenchyma continues, we will observe an involvement of pancreatic beta cells, responsible for the production of insulin - hypoglycemic hormone, which, following its release, will lead to a decreased blood sugar.
- blood count: another laboratory investigation that can guide us in the evaluation of an inflammatory picture through an increase in leukocytes (a condition known as leukocytosis).
- calcemia: blood calcium is reduced, with values below 8 mg / dL.
The assessment of calcium also has a prognostic role, as a reduction of the same is associated with a poor prognosis.
In addition to the acute manifestation of pancreatitis, there is also a chronic inflammation of the pancreas. It is associated with an impaired digestion of lipids and is characterized by steatorrhea - that is, the presence of lipids in the faeces, and is typically found in individuals who abuse alcohol.
Causes of chronic pancreatitis:
- genetic alterations
- tumors of the biliary excretory tract
- presence of stones
- autoimmune diseases
- cystic fibrosis
In the course of chronic pancreatitis, phases of exacerbation in which the dosage of amylase, lipase, trypsin and fecal elastase is recommended.
When to suspect pancreatitis?
When does amylase (blood amylase value) arouse suspicion for pancreatitis?
Values at least 3 times higher than the normal range are indicative of acute pancreatitis.
The sample used is blood. It will be obtained through a venous sampling, carried out in the patient who has fasted for at least 8 hours (therefore it is preferable to do it in the morning).
Kinetics of pancreatic hyperamylasemia
Amylasemia it usually peaks after 24 hours and normalizes within 3-4 days.
In some cases (representing about 5-30%), amylasemia values are also normal during pancreatitis, giving rise to a condition known as false negative - or negative test result despite the disease being present.
Contrary to false negatives, the condition in which the patient tests positive but does not have the disease is known as false positive.
These two conditions - namely false positives and negatives - allow to evaluate the sensitivity and specificity of a test, and therefore its reliability.
In the case of amylasemia, the sensitivity is around 75-92% and the specificity around 20-60%.
(The specificity appears to be so low since increased amylasemia values are not always attributable to acute pancreatitis, but may also be due to other diseases, as previously listed).
Together with the blood amylase assay (amylasemia), another parameter is often evaluated: amylasuria - that is the dosage of amylase in the urine.
Does macrolipasemia exist?
Nowadays, no forms of macrolipasemia have been highlighted, therefore the request for lipasuria is useless; nor is an increase in lipasemia considered attributable to the presence of macrolipasemia.
Renal alterations and changes in lipase and amylase values
Amylase and lipase are eliminated from the body through the kidney, therefore, alterations in renal function (eg acute or chronic renal failure) with consequent reduction of glomerular filtration rate can lead to an increase in amylasemia and lipasemia, although there is no pancreatitis in place.
Hypoamylasemia - Low amylases
Contrary to what was said previously, in this case we will observe a reduction in the amylase values. Low amylase is found predominantly due to pancreatic insufficiency or liver parenchyma abnormalities (eg liver cirrhosis), however isolated hypoamylasemia is not a concern.
THE normal values of lipase are: 0-55 U / L
For the diagnosis of acute pancreatitis, therefore, to the evaluation of amylasemia, the dosage of lipase, as it has greater sensitivity and specificity.
The values of lipase, in fact, they increase 4-8 hours after clinical manifestation, reaching a peak around 24 hours and a gradual decrease after 2 weeks.
The sensitivity of this test is found to be 86-100% and the specificity 50-99%, with a distinct advantage over amylasemia.
From this it follows that the amylase dosage should not be a routine test and that, today, it is often replaced by the dosage of lipases or in any case integrated with other blood tests.
Analyzes that can be prescribed in the presence of altered amylase values
- Complete blood count
- Electrolytes: Ssdium (Na), Calcium (Ca), Potassium (K)
- Total protein
- Pancreatic amylase
- Alkaline phosphatase
- Total and fractionated bilirubin
- LDH (lactate dehydrogenase)
- GT range
- Transaminases: AST and ALT
We can conclude by saying that certainly alterations in the amylase values can be consequent to pathologies affecting different organs, but which are mainly associated with alterations affecting the pancreas; and that their increase, especially for values three times higher than the normal range, must induce the suspicion of pancreatitis. However, this suspicion must be confirmed both by the clinical picture and by the alteration of other laboratory parameters.
In addition to laboratory investigations, a fundamental role in the diagnosis of pancreatitis is played by imaging techniques such as ultrasound of the abdomen, abdominal CT and cholangio-wirsung-MRI.
Tags: Enzymes Laboratory medicine Pancreas