Alanina Amino Transferase, ALT

Generality

Alanine amino transferase, more simply known as ALT or SGPT (serum glutamic pyruvic transaminase), is an intracellular enzyme present in many tissues, especially in striated muscles, in the brain and especially in the liver.

What's this

Alanino amino transferase (ALT, GPT or SGPT) is an enzyme that is found mainly in liver and kidney cells; to a lesser extent, it is present in the heart, muscles and skeleton.

In disorders causing damage to these tissues, the alanino amino transferase is released in greater quantities and enters the bloodstream.

Biological role

ALT is an enzyme belonging to the transaminase family, a group of proteins accumulated by the ability to catalyze the transfer reaction of the amino group (NH ₂ ) from an amino acid to an α-keto acid.

The one described above is a very important chemical reaction in the metabolism of body proteins, from the synthesis of new ones to the recovery of those already existing, from their use for energy purposes to the elimination of amino groups in the urea cycle.

Specifically, alanine amino transferase carries the amino group from alanine to alpha-keto-acid acceptor, transforming it into glutamic acid (the alanine deprived of the NH ₂ group is instead converted into pyruvic acid).

For sports enthusiasts, the SGPT is therefore an extremely important enzyme for the synthesis of glucose starting from alanine, an amino acid deriving from the metabolism of other amino acids, in particular those with branched chains (leucine, isoleucine and valine).

Why do you measure

The determination of ALT - SGPT is primarily useful as a liver function test .

Its serum content increases in front of any hepatic cell damage, up to the necrosis of the liver.

The specificity of this analysis is however low, in the sense that it gives us little information on the nature of the liver problem; however, we know that ALT levels are more sensitive in detecting hepatocyte damage (to liver cells) rather than biliary obstruction. Furthermore, as we shall see in a few lines, the simultaneous dosing of other enzymes allows obtaining additional information on the possible cause of the alteration.

Elevated ALT values ​​in the blood can also be observed following traumas and muscle diseases, as well as in myocardial infarction; for the diagnosis of these conditions, creatine kinase represents a more sensitive index.

When is the ALT examination prescribed?

The analysis of alanine amino transferase is indicated to evaluate liver damage and / or as a support in the diagnosis of hepatopathy.

When the liver is damaged, ALT is released into the blood, usually before the most obvious symptoms, such as jaundice (yellow skin and eyes), can occur.

Clearly, a wide variety of pathological conditions can result in impaired liver cells, with an increase in ALT. The examination of alanine amino transferase is particularly useful in determining the damage due to hepatitis, the use of hepatotoxic drugs or exposure to other toxic substances for the liver.

ALT is also used to monitor therapy in people with liver disease.

Associated examinations

Usually, the determination of ALT is required together with that of Aspartate amino transferase (AST), as part of the hepatic panel . The concentration of both these enzymes increases, in fact, every time the liver is damaged.

It should be noted, however, that alanine amino transferase is more specific for the liver than AST and, in some cases, may be the only one of the two liver enzymes to increase.

The AST / ALT ratio can be calculated to distinguish between the causes and severity of liver diseases and to discriminate between liver, heart or muscle damage.

To determine which form of liver disease is present, ALT values ​​are often compared to the results of other tests such as:

• Alkaline phosphatase (ALP);
• Total proteins;
• Bilirubin.

Normal values

In healthy individuals, blood alanine amino transferase levels are low.

REFERENCE VALUES ALANINE AMINO TRANSFERASI

• MAN: up to 50 U / L
• WOMAN: up to 40 U / L

ALT High - Causes

An increase in ALT in the blood may be due to liver disease, obstructive jaundice, heart attack, hypothyroidism and liver metastasis.

ALT very high

• Acute liver injury (viral, alcoholic, autoimmune, drug, etc.);
• Tumor necrosis (as can occur in the presence of a primitive liver cancer or secondary metastases of other neoplasms, especially prostate or colon).

ALT moderately high

• Chronic liver disease (chronic hepatitis / cirrhosis, primitive sclerosing cholangitis and primary biliary cirrhosis);
• Obstructive jaundice;
• Alcoholism;
• cholestasis;
• Cardiac damage (myocardial infarction or heart failure);
• Acute kidney damage;
• Muscle damage or injury (intense physical effort or trauma);
• Hemolysis;
• Heat stroke;
• High vitamin A consumption;
• Mononucleosis;
• Cytomegalovirus infection.

ALT slightly elevated

• Hepatic steatosis;
• Low-activity liver cirrhosis;
• Taking certain medications;
• Pregnancy.

ALT Low - Causes

A reduction of the alanine amino transferase may be due to:

• Vitamin B6 deficiency;

• Habitual muscular exercise.

How to measure it

The examination is performed with a normal collection of peripheral blood from the vein of an arm.

Preparation

Before taking a blood test for the ALT test, it is necessary to observe a fast of at least 8-10 hours. During this period, it is only possible to take a small amount of water.

Also, before the exam, you must be in an upright position for at least 30 minutes.

Interpretation of Results

• Normally, the ALT concentration in the blood is low.
• Markedly elevated ALT values ​​are usually caused by acute hepatitis, often caused by a viral infection. The concentration of ALT can be very high even as a result of exposure to drugs, drugs or other liver-toxic substances, or in conditions that cause a decrease in blood flow to the liver (ischemia).
• Causes of moderate ALT increase include: obstruction of the biliary tract, cirrhosis, heart damage, alcohol abuse and liver tumors.
• ALT is often required together with the AST or as part of the liver test panel.

Causes of High and Low ALT

Correlation with other analysis and interpretation

In addition to ALT, a very important transaminase is AST (Aspartate aminotransferase), a mitochondrial and cytoplasmic enzyme which, similar to ALT, is present in hepatocytes but also in non-hepatic tissues, where it is however in greater proportions than the ALT.

It follows that in myocardial infarction the ALT levels increase to a lesser extent than those of the AST.

The AST / ALT ratio also increases in liver alcoholic diseases, cirrhosis and musculoskeletal injuries.

• HEPATOCELLULAR LESIONS: increase in ALT, AST, predominantly indirect bilirubin and, to a lesser extent, lactate dehydrogenase.
• COLESTASI: consistent increase in alkaline phosphatase (ALP) and GT-range.

As shown in the figure, the degree of increase in ALT values ​​is also an important diagnostic clue.