Aspartate Aminotransferase (AST)
Liver Function Tests
Liver function tests as the name suggests is the assembly of vivid blood plasma tests which aid in identifying any kind of inflammation or impairment done to liver. Testing of Liver enzyme plays a crucial role in the diagnosis of the liver disease and the various enzymes which are subjected to the test consist of enzymes like alkaline phosphatase, ALT, AST, albumin INR, bilirubin and PT.
The liver test is used to identify the levels of enzyme and proteins in the blood. The enzymes which can be detected using the test are bilirubin, alkaline phosphatase, aspartate amino transferase and amino alanine transferase .Apart from that it can also be used to inspect the various proteins such as LDL, albumin and globulin in blood.
Why Check Liver Function?
The Liver test is detrimental and a very important for the identification of the various diseases which hamper the liver. But above all your physician can order the liver test during instances such as:
- Person showing abdominal pain, nausea yellowing of skin or vomiting.
- If someone is on a medication for some other disease which has the side effect to liver too.
- Excessive intake of alcohol
- Alternatively if someone has a specific liver disease as well.
There are various liver tests that can be done alone or in combination with each other.
What are the main functions of liver?
The liver which is the largest internal organ acts as a filtering agent and helps in processing and circulating the blood in the whole body. But apart from that it has variety of important functions to carry which is briefly described as under.
- Metabolism/Digestion of the various nutrients
- Formation of Blood clotting proteins.
- Decontamination of the substances injurious to the whole body.
- Production of Bile which aids in the digestion of lipids.
- Production of albumin
- Production of Bilirubin protein
To understand the anatomy of liver it’s essential to know about various enzymes present in the liver. The liver cells contain variety of enzymes which act as a catalyst in driving the various chemical reactions taking place in the body and are the agents behind carrying out any biological reaction.
A broken/impaired liver cell leads to the oozing out of enzymes in the blood which in turn can be used as an indicator in the liver test.
The main enzymes which are identified in the blood test are AST (Aspartate aminotransferase) and ALT (Alanine aminotransferase).
- Aspartate aminotransferase enzyme is found in muscle cells apart from the liver cells.
- Other crucial enzyme like Alanine aminotransferase is found solely in the liver cells and is useful in detecting the liver disease.
What does the test tell?
The elevated or raised levels of both the enzymes ALT and AST is an indicator of the liver damage and helps in identifying the various disease associated with the liver .For instance a raised level of any of the following enzyme surely indicates liver damage and is a thing to look upon with utmost importance.
Liver Enzyme Tests: Alkaline Phosphatase, 5’ Nucleotides, and GGT
The element which plays crucial role in this study is the Bile which is a fluid secreted by liver and is stored in the gallbladder and helps in the emulsification, absorption and digestion of Lipids. An obstructed or jammed bile flow will increase the level of some liver enzymes such as alkaline phosphatase, 5' nucleotides and Gamma-glut amyl Tran’s peptidase (GGT)
A raised or elevated level of any of the above mentioned enzymes is the true indicator of malfunction of the liver or the gallbladder and the tubes connected with them.
Liver Function PT and INR test for checking the blood coagulation or clotting
Liver aids in blood clotting by the production of clotting proteins such as Prothrombin. The test is used to determine the liver’s capability in efficient production of these proteins. The test include
Prothrombin time (PT): This test checks the ability of the blood to clot in a specified time. The blood sample is kept for some time to clot and the duration of the clotting is identified .If the time taken to clot is longer which indicates low levels of the clotting proteins. International normalized ratio (INR): Is a common test performed in various labs to check the Prothrombin levels and is useful in comparison of the results obtained thereafter.
- The combination of both the PT and INR helps in identifying the problems related with blood clotting and an increased in the level of these proteins is an indication of malfunction of the liver and its inability to make the normal levels of these proteins.
Liver Function Tests: Albumin
The liver is also responsible for the generation of very important protein known as albumin which flows along with the blood. A rise or fall in albumin levels doesn’t necessarily indicate the liver damage alone but is helpful in diagnosing various other anomalies in the body too. The low levels of albumin indicate a prolonged or severe liver disease.
Liver Function Tests: Bilirubin
The waste or unused product Bilirubin is formed during the haemolysis of the RBC and liver acts on the protein and breaks it down and is then transported through the Liver’s bile duct out of the body through the faeces. .
What does the raised Bilirubin level indicate?
- Impaired bile flow/Malfunctioning of the Bile ducts
- Chronic liver or gallbladder disease
- Jaundice which cause the yellowing of the skin and the sclera.
- Presence of haemolytic anaemia
Aspartate Transaminase (AST/GOT/SGOT) Test
An (AST) test is also an important test and helps in identifying the various ailments related to liver or helps in identifying the disease related to Liver.
Aspartate Transaminase (AST) belongs to aminotransferase family and it catalyses the (reversible transfer of the amino group from glutamate to oxaloacetate with the replacement of amino group with a carbonyl group which is done in the presence of a cofactor pyridoxal-5’-phosphate (P5P)
This cofactor plays an important role in the reaction in the transfer of the carbonyl compound by accepting the amino group.
.AST is not found in urine but present in almost every tissue and fluid in the human body and also in vital organs such as liver, kidneys, and pancreas and skeletal muscles. A dysfunction of any organ may release the AST in the blood. So it cannot be solely considers to test the liver damage. Two forms of AST exist which are cytoplasmic and mitochondrial enzyme. The detection of levels of AST helps in understanding the pathological condition associates with various organs and largely for the malfunction of the liver.
What does the rise of AST indicate?
The rise can be attributed to heart diseases such as myocardial infarction but couldn’t be solely taken into consideration for diagnosing the heart attack....
Another enzyme known as ALT (alanine aminotransferase) is found in abundance in the liver. The Alt is measured using indirect enzymatic method. The transamination reaction is not characterized by any useful spectrophotometric change. The technique deployed here is to couple a reaction site product with the other product of a reaction which in turn will reduce or oxidizes NAD+/NADH accordingly.
However, when physician looks at the blood levels of AST its easier for him/her to diagnose any problems surrounding liver functioning or damage and the diseases which may affect liver or other organs.—
Aspartate transaminase is known as (AspAT/ASAT/AAT) or by serum glutamic oxaloacetic transaminase (SGOT), plays an important role in amino acid metabolism .It is a pyridoxal phosphate (PLP)-dependent transaminase enzyme which catalyses the reversible transfer of an α-amino group between aspartate and glutamate . AST is found in the liver, heart, red blood cells, skeletal muscle, brain, kidneys and plays an important role in analysing the diseases related with liver and is used frequently as a test in most of the clinics around the world.
The mechanism or the functioning of the Aspartate transaminase can be summarized as under
Aspartate transaminase works by catalysing or converting a separate and α-ketoglutarate to form oxaloacetate and glutamate. The chemical reaction for the same is under.
Aspartate (Asp) + α-ketoglutarate ↔ oxaloacetate + glutamate (Glu)
AST which is a prototypical transaminase works by transferring amino group from aspartate or glutamate to the corresponding ketoacid with the aid of a cofactor known as PLP.The process takes place by the PLP acting as a shuttle and engages between pyridoxine phosphate (PMP) and PLP form. This type of catalysis is essential for both the biosynthesis and amino acid degeneration. By this the amino acid degradation, takes place by oxidative deamination by glutamate to form ammonium ions which at last is excreted out of the body through urine. The oxaloacetate which is formed from aspartate in the reverse reaction plays important role in the citric acid cycle.
The isoenzymes is present in diversity among the various eukaryotes and in humans beings the isoenzymes which is present in abundance are as follows
- GOT1/cAST which is also known as the cytosolic isoenzymes originates mainly from the cells of heart and the blood.
- GOT2/cAST is known as the mitochondrial isoenzymes and is found in surplus in the cells of the liver.
These isoenzymes have descended from the same ancestral AST and have common homology sequence and are evolved as a result of gene duplication. AST can be traced or is found in abundance in a variety of microorganisms present around us such as H. Mediterranean, E.coli etc. In E. coli AST enzyme is present in an encoded form and also shows the activities similar to the amino acid known as transaminase.
To understand the functioning of the enzyme it’s important to have an overall review of the Structure of the enzyme known as the aspartate transaminase.
Till date many experiments have been done such as X-ray crystallography studies which has been detrimental to identify the structure of aspartate transaminase and has been done on various sources, including mitochondria of a chicken ,cytosol of the heart of a pig or the E.coli . But the result depicted in all the test shows the similar three-dimensional polypeptide structure for all species. AST has a molecular weight of around 45 KD and has a diametric structure. It consists of two identical subunits with chains of around 400 amino acid molecules.
Each subunit is again divided into three parts containing large domain 48-325, small domain of residues 15-47 and 326-410, as well as a third domain consisting of the N-terminal residues 3-14;To stabilize the dimer these residues form a strand, which links and stabilizes the various units of the dimer.
The two active sites are located near the border amid the two domains. Inside each active site, a pair of arginine residues is present which is responsible for the enzyme’s specificity for dicarboxylic acid substrates.
Arg386 interrelates with the substrates proximal (α-) carboxylate group, while Arg292 multiplexes with the distal (side-chain) carboxylate.
The other structure of AST have α and β elements. Each domain consist of central sheet of β-strands with α-helices attached on either side of the strands
The working of Aspartate transaminase is through dual substrate recognition in which the transaminase binds the amino acids with the side chains .The amino acid which participates in this are Asp and Glu. The whole mechanism takes place through half reactions and is known as the ping pong mechanism. The first half-reaction results in the generation of oxaloacetate) from the reaction between L-Asp) and enzyme-PLP complex, In the second half-reaction, (α-ketoglutarate reacts with enzyme-PMP to produce amino acid 2 (L-Glu),
The mechanism results in the formation of many bye products which include aldimine, Quinonoid, Ketamine .The ketamine in turn again undergoes the hydrolysis process to form the PMP and Oxaloacetate which plays.
The reaction proceeds by formation of aldimine internally by the linkage between the amino groups with Schiff base.
The Transaldimination reaction happens through nucleophilic attack by the amino group as this point, the carboxylate groups of Asp is steadied by the guanidinium groups of the enzyme’s Arg386 and Arg 292 residues.
The Quinonoid is generated by the attachment of the hydrogen element with that of the a-carbon of Asp
The ketamine formation is a simple process which takes place through the reprotanation at the aldehyde linked carbon site. As soon the ketamine is formed it enters the final stage where it will be hydrolysed and form the last final product of this cycle which is PMP and Oxaloacetate.
This mechanism is seen to have many side by side rate determining steps but it has been observed that the Transaldimination is the main step which drives the reaction forward and is considered as the main step which aides in driving the reaction ahead alone. Reaction forward.
What is the Clinical significance of AST?
In 1954 AST was used as the main biochemical for early recognition of the heart disease known as the myocardial infarction .But with the recent advancements in the science and techniques its role in determining the infarction is dismissed and has been taken
Over by the various troponins which are best suited to identify the infarction.
The AST is same as ALT as both are related or present in the liver cells more specifically the parenchymal cells of the liver. The main difference lies in the place of origin where ALT is solely found in the Liver cells and less amounts in the other vital organs such as the kidneys, heart and skeletal muscles but in contrast AST can be tracked in measurable quantities in liver as well as in other organs in the body.
The ALT can be used as the best tool to measure any kind of inflammation present in the liver than the AST as the elevated level of AST can also be related to various other clinical anomalies other than liver dysfunction such as myocardial infarction, haemolytic anaemia, musculoskeletal diseases, renal disease and acute pancreatitis and chronic alcoholism.
What is the reference range for the AST test? The reference range used in this test includes
- Female its around 6 - 34 IU/L
- Male its around 8 - 40 IU/L
Aspartate aminotransferase is one of the essential liver enzymes of the two essential enzymes. The enzyme is also known as serum glutamic-oxaloacetic transaminase which is a protein and is first generated by the liver and when the liver cells are destroyed the enzyme oozes out of the liver and is thrown in the blood vessel and in such condition the AST level shows a sudden increase than the normal levels, which is expected to be present in the blood. The AST elevation in the blood cannot be attributed to the liver alone it can be produced in abnormal concentration by the other organs of the body as well such as the kidneys, muscles, heart and brain. So that means any damage to these organs may also constitute a rise in the level of blood AST.
What can be interpreted by the results?
There are various conditions which can be attributed to the levels of AST and can further be divided into three subheads which are as under.
The first condition depicts a very high level of the aspartate aminotransferase which is 10 times more than the normal values depicts the following ailments.
- Liver damage
- Acute hepatitis
- Tumour necrosis
- Toxins/drugs overdose
- Extreme form of viral hepatitis
The second condition is a moderately high aspartate aminotransferase level which can lead to the following diseases.
- Pulmonary embolism
- Heatstroke (the extent depending on the tissue damaged)
- Chronic liver disease
- Alcohol abuse
- Muscle injury (muscular dystrophy, dermatomyositis, trauma)
- Over intake of vitamin A
- Kidney damage
- Heart damage such as heart attack or heart failure in extreme cases.
The third condition to be studied is the slightly high levels of the Conditions associated aspartate aminotransferase and which can lead to the following diseases.
- Alcohol abuse
- Fatty change in the liver
- Use of Drugs such as aspirin, statins, barbiturates, herbs and HIV medication,)
Collection and Panels used in the Test are:
The specimen used is the Blood Serum and is collected in the Red Top tube.
AST the enzyme which is found in the liver and heart in good concentration and can be found in various other tissues as well like the brain, muscle, red blood cells, pancreas, kidneys and brain etc. Any damage to theses organs or the haemolysis may lead to the release of the enzyme which results resulting in increased AST levels in the serum. Serum levels generally parallel the extent of damage.
Another enzyme known as the alanine aminotransferase or ALT is mainly found in abundance in the cells of the liver. AST and ALT together is used to determine the liver damage and is measured together as part of a liver function panel to detect liver damage. Liver diseases in which AST is higher than ALT include alcohol-induced liver damage, cirrhosis, and liver tumours. AST formerly was called serum glutamic oxaloacetic transaminase (SGOT). Aspartate transaminase catalyses the conversion of aspartate and α-ketoglutarate to glutamate and vice versa. The reaction can be summarized as under.
Aspartate (Asp) + α-ketoglutarate ⇌ oxaloacetate + glutamate (Glu)
An aspartate aminotransferase (AST) test measures the level of the enzyme AST in the blood. AST is found in red blood cells, liver, heart, muscle tissue, pancreas, and kidneys. AST was previously also known as serum glutamic oxaloacetic transaminase (SGOT).
Normally Low levels of AST are present in the blood. When body tissue or organ such as the heart or liver is damaged .AST become visible in the blood cell. The presence of AST in the blood depicts the extent to which the tissue is damaged. The rise in AST level takes place for 6 to 10 hrs. and lasts for another 4 days.
The AST test can be done at the same time as the ALT test as both the ratio of AST to ALT helps in determining the level of damage done to the liver or any other organ.
What does the test indicates?
The AST test is done for the diagnosis of the liver disease and the various common symptoms which are seen during the liver damage are
- Dark urine
- Pale colored stools
- Loss of appetite
- Abdominal pain
- Mental changes,
- History of alcohol abuse
- Suspected acetaminophen overdose
- family history of liver disease
- Exposure to hepatitis viruses).
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The AST test is also used to monitor the liver function during
the use of drugs which are injurious to liver check hemochromatosis treatment or to check the status of chronic liver disease, , alcohol-induced liver disease ,hepatitis, cirrhosis, fatty liver disease, hepatic failure, Wilson’s disease and many other medical ailments.
- The determination of alcohol-induced liver disease can be done through the AST test. If
The AST:ALT ratio also known as the (De Ritis ratio) ratio is greater than 2 it depicts the alcohol induced disease of the liver..
- In a person suffering from acute hepatitis AST levels are usually seen to stay higher for around 1–2 months and can also take as long as 3–6 months to return to normal.
- In chronic hepatitisthe AST levels don’t appreciate much it seen to remain, often less than 4 times the highest normal level.
- Such increases can be seen if there is a blockage in the bile ducts or when there exist certain cancers of the liver cell.
- AST level shows a rise during the injury or attack in the myocardial cells which lead to the heart attack
AST and ALT results directly depends on the vitamin B6in the body also. For accurate AST and ALT results the amount or the level of Vitamin B6 plays a crucial role if there is a reduction in the Vitamin B6 level it can lead to artificially low AST and ALT levels.
- During pregnancy the AST levels decrease
- Muscle injections and strenuous exercise can lead to muscle damage which in turn increases the AST levels.
- Haemolysed specimens should not be considered.
- AST remains stable at a temperature of around 4 º C for a span of 48 hours.
Why the Test Is Performed
An aspartate aminotransferase (AST) test is performed in the following situations
- To rectify the liver disease such as hepatitis and cirrhosis. Liver disease may produce symptoms such as pain in the upper abdomen, nausea, vomiting, and sometimes jaundice.
- To check if there is any damage done to the liver.
- To check the success of treatment if visible for any liver disease.
- To find if the cause of jaundice was blood disorder or liver disease.
- To keep a record of the effects of cholesterol-lowering medicines and other medicines this can hamper or damage the liver.
- If a child is experiencing jaundice (yellowish skin or eyes), dark urine, nausea, vomiting, or abdominal swelling.
- . It may also be ordered to help diagnose infections of the liver such as viral hepatitis, or to monitor patients taking medications that can cause liver-related side effects.
The AST test is frequently accomplished as a portion of a full hepatic function panel which includes other liver enzyme tests also The physician can refer the AST levels along with those of other liver enzymes — such as ALT and alkaline phosphatase (ALP) for framing a clear picture regarding the liver damage or disease associated with it.
No prior preparation is needed for performing the AST test. The physician should be well informed regarding the medications a person is taking because it is seen that certain medications can alter the results of the test.
AST Test is performed by analysing the blood sample which is taken by obtaining an intravenous access to the site which is an elbow bend.
The organs which contain AST are liver, heart skeletal muscle, pancreas, kidney, lung, spleen, red blood cells, and brain tissue. When there is a disease or injury which affects the tissues of these cells, the cells of these organs experience a rupture and AST comes out of it into the bloodstream. The amount or rise of AST in the blood largely depends on the duration or period of time when the blood is tested after injury and the level of AST is directly proportional to the number of cells affected by the disease or injury. The elevation or rise in the Plasma AST levels is seen eight hours after cell injury and highest at 24-36 hours, and reappear to normal in three to seven days. If the cellular injury is severe and long lasting AST levels will be at its highest peak.
For many years the AST determination has been fruitful in the diagnosis of heart attacker MI. AST can also help in determining the timing and extent of a recent MI, If there is no further cardiac injury the rise in AST level takes within 6-10 hours after an attack and it peaks at 12-48 hours, and returns to normal in three to four days. The injury to the myocardial cells known as angina (chest pain) or pericarditis (inflammation of the pericardium, the membrane around the heart) will not show the raised AST levels
AST proves to be a valuable and important kit for the diagnosis of the various liver diseases and can be used in accordance with other enzymes to screen the course of various liver disorders.
The severe and silent hepatitis (hepatitis C) is also caused due to the rise in the level of AST.
A moderate rise in the level of the AST can be attributed to alcoholic hepatitis, which takes place due to excessive alcohol intake.
In acute viral hepatitis AST levels are moderately elevated and the rise in AST levels is seen around 20 times more than usual.
Acute extra hepatic which takes place outside the liver like gallstone is seen to have elevated AST levels by 10 times than the normal AST level and fall thereafter again.
During cirrhosis there is inflammation of the liver and the rise in AST level is directly related to the amount inflammation.
The AST Determination proves to be effective for the early recognition of the condition hepatitis which can originate from exposure to toxic drugs like acetaminophen and cholesterol lowering medications which are injurious to the liver.
The diagnosis of AST is also helpful if you are suffering from any of the following disease such as acute pancreatitis, severe burn, trauma, muscle disease, and infectious mononucleosis etc.
The blood test (AST) is generally done to diagnose any injury or damage caused to the liver and is done along with the other liver enzyme which solely persists in liver i.e. the ALT or the alanine aminotransferase (ALT).
AST and ALT tests are the best test in the category of test to diagnose the liver dysfunctions as these test aids in identifying the ailments of liver malfunction or any damage done to it. ALT is more specific than AST test
In some cases a comparison of AST is done with the ALT and an AST/ALT ratio is calculated. This ratio can help in identifying the causes of the liver damage.
The AST levels frequently compared to the other test done for the detection of liver damage which are alkaline phosphatase (ALP), total protein, bilirubin which aids in determining the extent of liver damage done by the various disease.
AST is often used to monitor or treat suffering from various liver diseases and is done alone or in combination with other test to identify the liver damage.
Most of the times AST is used to keep the track of the people taking medications that are highly toxic to the lever. The person should be switched to another medication if AST level goes high.
While taking blood sample from vein there is very little chance for problem.
There is very less risk in this test but it may include the blood accumulating under the puncture site or slight bleeding from the blood drawing site.
On site you may get a small bruise, to lower the chance of bruising keep the pressure on the site for several minutes.
It rarely happens that you get swelling on vein after taking the blood sample. This problem is called phlebitis. To treat this warm compress can be used several times in a day.
On-going bleeding can cause a bleeding disorder. You should inform doctor if you have clotting or bleeding problem, or if you consume a blood thinning medicine before he takes a blood sample.
AST measures the amount of this enzyme in the blood. Within 12 hours the result will be available usually.
Other things to know:
- As compare to ALT level AST level is not helpful for checking the liver.
- Most of the hepatitis C patient has normal AST level.
- Patients with severe liver disease can still have normal AST level.
The normal value listed below can differ lab to lab. It depends on the range the labs uses. Also the doctors evaluate the result on the health or other factors. This means the value other than below mentioned normal value can also be a normal level for you according to different lab
14-20 units per liter (U/L) or 0.23-0.33 microkats per liter (mckat/L)
10-36 U/L or 0.17-0.60 mckat/L
High levels of AST may be caused by liver damage from conditions such as hepatitis or cirrhosis, decay of a large tumour, a heart attack or heart failure, many medicines, such as statins, antibiotics, chemotherapy, aspirin, narcotics, and barbiturates, taking high doses of Vitamin A, kidney or lung damage, mononucleosis or some types of cancer.
What are the causes of Elevated or High SGPT & SGOT?
Liver function tests like SGPT, SGOT, serum alkaline phosphatase, Australia antigen, globulin and albumin indicates the liver malfunction and the various ailments attached with it.
The main reason for the undertaking the tests are as follows. =
- The test also helps to estimate the liver damage and used as a guide for treating and knowing the prognosis of the liver disease.
- To assist in differentiating whether the jaundice can be treated in a medical conservative way, for example in case of viral hepatitis, or it requires surgical treatment, as in case of obstructive jaundice due to gall bladder stones.
- For confirming the suspected liver disease.
Irrespective of the cause, Liver functions are not impaired to the same degree in any one case of liver disease.
SGPT and SGOT are the most important enzymes of the liver parenchymal cells. They are in large numbers in the liver. These enzymes are released in the blood when the liver cells get damaged.
You will have to get further investigation done such as test for hepatitis C, B, and E. Also get a solography of the abdomen done.
Causes of Increased SGOT Levels
Causes are almost same as in SGPT rise, but in acute myocardial infarction, only SGOT gets increased.
For early detection of infective hepatitis, these enzymes are very important markers.