View source for Biochemical examination of the pancreas

=== α-amylase ===
[[File:3-D Structure of Alpha-amylase.png|thumb|Pancreatic amylase]]

'''α-amylase''' <ref>{{Cite|type=article
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<ref>{{Cite|type=article
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|article=Recommendations for the routine use of pancreatic amylase measurement instead of total amylase for the diagnosis and monitoring of pancreatic pathology
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<ref>{{Cite|type=article
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|article=Evaluation of amylase and lipase in the diagnosis of acute pancreatitis
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<ref>{{Cite|type=article
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<ref>{{Cite|type=article
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|article=A comparison of lipase and amylase in the diagnosis of acute pancreatitis in patients with abdominal pain
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<ref>{{Cite|type=article
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<ref>{{Cite|type=article
|surname1=Malfertheiner|name1=P
|surname2=Enrique Domínguez-Muñoz|name2=J
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}}</ref> ('''AMS''', α-1,4-glucan-4-glucan hydrolase, EC 3.2.1.1) hydrolyses [[α-1-4-glycoside bond]]; The [[pH]] optimum of α-amylase is between 7.0-7.2. It occurs in the body in two forms - according to its organ origin as salivary and pancreatic [[isoenzyme]]s. Both isoforms of AMS differ from each other by the sugar component and can be distinguished electrophoretically or by precipitation using a special [[lectin]] or [[antibody|antibodies]] <ref>{{Cite|type=book|name1=Jaroslav|surname1=Racek|others=yes|title=Klinická biochemie|edition=2|publisher=Galén|place=Praha|year=2006|isbn=80-7262-324-9|volume=329|pages=87}}</ref>. α-amylase is produced by the acinar cells of the [[pancreas]] and accumulates in its zymogenic granules. It enters the intestinal lumen as a part of pancreatic secretion ([[pancreatic juice]]) along with other [[digestive enzyme|digestive enzymes]]. Under physiological conditions, [[enzyme|the enzyme]] molecule is not absorbed by the intestinal surface and the serum level is low. It corresponds to the activity of the enzyme released into the circulation directly from the glandular cells (lymphatic drainage). The molecular weight of α-amylase is 55,000. Α-Amylase is eliminated from the circulation in the kidneys by [[glomerular filtration]].

The macro form of the enzyme (''macroamylase'')
<ref>{{Cite|type=article
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<ref>{{Cite|type=article
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<ref>{{Cite|type=article
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<ref>{{Cite|type=article
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<ref>{{Cite|type=article
|surname1=Hortin|name1=GL
|surname2=Summerfield|name2=AL
|surname3=Wilhite|name3=TR
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|url=http://clinchem.aaccjnls.org/content/clinchem/40/12/2254.full.pdf,
}}</ref> is formed by the bondage of the enzyme to certain blood serum proteins, especially [[immunoglobulins]], circulating immunocomplexes, or other [[glycoproteins]]. The macro form of the enzyme has a significantly higher [[molecular weight]] (from 150,000 to 2,000,000) and is therefore not eliminated by glomerular filtration in kidneys. For clinical diagnosis serum and urinary α-amylase levels are determined and the amylase/[[creatinine]] [[clearance]] index is calculated.
[[File:Amylase reaction.png|thumb|Amylase hydrolysis reaction]]

The [[protein]] concentration can be determined by [[immunological techniques]] or enzyme catalytic concentration using specific substrates. The presence of inhibitors in serum and the formation of enzyme macro forms should be considered when determining both [[mass|mass concentration]] and [[catalytic concentrations]] of the enzyme. The commonly used determination of α-amylase activity is based on the fission of a chromogenic substrate. Older processes that used derivatives of the natural substrate ([[starch]]) were difficult to standardize and are no longer used. Current synthetic substrates are derived from [[maltose]]. The most commonly used is [[chromogen]] [[4-nitrophenyl phosphate]]. The determination of α-amylase isoenzymes is made possible by the inhibition of one of the two isoenzymes by a specific [[monoclonal antibody]].

In the most common arrangement, the salivary isoenzyme amylase is inhibited first by the antibody in the sample. The reaction is started by adding a '''substrate protected by ethylidene''' – glucose heptamer which is bound to one end and a chromogen is at the other end of ethylidene. Amylase from the sample hydrolyzes the oligoglucoside chain. The coloured nitrophenol is then released by the reaction of another component of the reaction mixture, '''glucosidase'''. Because α-glucosidase can only cleave end-chain glucose and does not recognize ethylidene-protected glucose, a substrate that has not been hydrolyzed by amylase is protected from the effect of glucosidase <ref>{{Cite|type=web|corporation=Roche Diagnostics|source_name=Pankreatická α-amyláza EPS (AMY-P)|url=http://www.roche-diagnostics.cz/objednavky/info/20766623pi.pdf|cited=2010-04-09|date_of_revision=2009-01}}</ref>.

; Reference values <ref>{{Cite|type=book
|corporation=Všeobecná fakultní nemocnice v Praze
|name1=Tomáš|surname1=Zima
|otheres=yes
|title=Přehled laboratorních vyšetření prováděných ve Všeobecné fakultní nemocnici v Praze
|year=2007|publisher=Všeobecná fakultní nemocnice v Praze|edition=3|place=Praha|volume=328
|isbn=-
}}</ref>
:: '''S-AMS''' total serum amylase '''0.30–1.67 μkat/l'''
:: '''U-AMS''' total urinary amylase '''<7.67 μkat/l'''
::'''S-pAMS''' pancreatic amylase in serum '''0.22–0.88 μkat/l'''
:: '''U-pAMS''' pancreatic urinary amylase '''<5.83 μkat/l'''
::'''macroamylase undetectable'''

'''Interpretation of findings''' 
From a practical point of view, an increase in serum α-amylase activity is an important finding. It can be caused by:

* '''increased amylase release''' from damaged pancreatic or salivary gland cells or
* '''by reduced glomerular filtration''', where this small protein is filtrated into the primitive urine to a lesser extent than usual.

'''Hyperamylasemia''' in damaged pancreas or salivary glands is accompanied by an increase in urinary amylase activity when normal renal function is present; however, it is necessary to take into account that it appears in the urine with a delay of several hours. In this case, it remains to distinguish whether amylase comes from the pancreas or salivary glands. If a decision cannot be made on the basis of the clinical picture, the determination of isoenzymes will give an answer.

Decreased glomerular filtration of amylase is most often due to renal insufficiency. In this case, hyperamylasemia will be accompanied by low urinary concentration and amylase activity. Another, much rarer cause of decreased renal amylase clearance, is macroamylasemia.