Muhammad Asif Zeb Lecturer MLT IPMS,KMU

Measurements of the activity of enzymes in plasma are of value in the diagnosis and management of a wide variety of diseases.

Small amounts of intracellular enzymes are present in the blood as a result of normal cell turnover.

When damage to cells occurs, increased amounts of enzymes will be released and their concentrations in the blood will rise.

However, such increases are not always due to tissue damage.

Other possible causes include:

increased cell turnover

cellular proliferation (E.g. neoplasia)

increased enzyme synthesis (enzymes induction)

obstruction to secretion

Enzyme assays usually depend on the measurement the catalytic activity of the enzyme, rather than the concentration of the enzyme protein itself.

One international unit is the amount of enzyme that will convert one micromole of substrate per minute per litre of sample and is abbreviated as U/L.

A major disadvantage in the use of enzymes for the diagnosis of tissue damage is their lack of specificity to a particular tissue or cell type.

Many enzymes are common to more than one tissue.

Alanine transaminase or ALT is a transaminase enzyme (EC 2.6.1.2).

It is also called serum glutamic pyruvic transaminase (SGPT) or alanine aminotransferase (ALT).

ALT is found in serum and in various body tissues, but is most commonly associated with the liver.

It is the reaction between an amino acid and an alpha-keto acid. The amino group is transferred from the former to the latter;

this results in the amino acid being converted to the corresponding α-keto acid, while the reactant α-keto acid is converted to the corresponding amino acid.

Transamination in biochemistry is accomplished by enzymes called transaminases or aminotransferases.

This process is an important step in the synthesis of some non-essential amino acids (amino acids that are not supplied from the diet).

More specifically, AST, ALT, and alkaline phosphatase are called the liver enzymes and they typically are

used to detect damage or injury to the liver (not its function).

ALT is exclusively in cytoplasm of many tissue like liver, heart, kidney, lungs.

But highest concentration is present in liver.

It is commonly measured clinically as a part of a diagnostic liver function test, to determine liver health.

Diagnostically, it is almost always measured in

units/liter (U/L).

Normal level in serum:ALT < 45 units/ml

Elevated levels:

Viral or autoimmune hepatitis.

Cirrhosis.

Lack of blood flow to the liver (liver ischemia). Death of liver tissue (liver necrosis). Liver tumor. Use of drugs that are poisonous to the liver.

Biliary duct problems.

For this reason, ALT is commonly used as a way of screening for liver problems.

When elevated ALT levels are found in the blood, the possible underlying causes can be further narrowed down by measuring other enzymes.

For example, elevated ALT levels due to liver-cell damage can be distinguished from biliary duct problems by measuring alkaline phosphatase.

The Alanine Transaminase (ALT) spectrophotometric assay uses enzymatic reaction:

GPTL-Alanine + α-ketoglutaric acid L-Glutamic acid +

Pyruvic

LDHPyruvic acid + NADH + H+ L-Lactic acid +

NAD+

The absorbance is measured at 505 nm, is proportional to the level of ALT enzyme in the sample.

Why Get Tested?To screen for liver damage and/or to help diagnose

liver disease.

Sample Required?Serum.

When is it ordered?To evaluate a person who has symptoms of a liver

disorder: Weakness, fatigue, Loss of appetite Nausea, vomiting Abdominal swelling and/or pain Jaundice Dark urine, light colored stool Itching (pruritus)

What does the test result mean?

Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute hepatitis, often due to a virus infection.

In acute hepatitis, ALT levels usually stay high for about 1–2 months but can take as long as 3–6 months to return to normal.

ALT levels are usually not as high in chronic hepatitis, often less than 4 times the highest normal level.

Other causes of moderate increases in ALT include obstruction of bile ducts, cirrhosis and with tumors in the liver.

In most types of liver diseases, the ALT level is higher than AST.

Aspartate transaminase (AST) also called serum glutamic oxaloacetic transaminase (SGOT) (EC 2.6.1.1) is similar to alanine transaminase (ALT) in that it is another enzyme associated with liver parenchymal cells.

Two isoenzymes are present in humans.

GOT1, the cytosolic isoenzyme derives mainly from red blood cells and heart.

GOT2, the mitochondrial isoenzyme is predominantly present in liver.

Normal Level:AST <40 units/ml

It is raised in acute liver damage. It is also present in red blood cells and cardiac muscle, skeletal muscle and may be elevated due to damage to those sources as well. AST was defined as a biochemical marker for the diagnosis of acute myocardial

infarction in 1954. However the use of AST for such a diagnosis is now redundant and has been superseded by the cardiac troponins.

AST (SGOT) is commonly measured clinically as a part of diagnostic liver function tests, to determine liver health.

Glutamic-Pyruvic Transaminase (GPT) is found in significant quantities in liver, kidney, and skeletal muscle, in decreasing order.

When liver cells are damaged, GOT and GPT levels rise especially early in the disease.

In hepatitis, transaminase levels rise several days before jaundice begins.

The enzyme levels are especially useful in assessing subtle and early changes in biliary obstruction and active cirrhosis.

Principle: GOTL-Aspartate + α-ketoglutarate L-Glutamate +

Oxaloacetate

The oxaloacetate obtained is measured in its derative from 2,4 dinitropheny hydrazone.

The absorbance is measured at 505 nm, is proportional to the level of ALT enzyme in the sample.

Sample:Serum.

Glutamic-Oxaloacetic Transaminase (GOT) occurs in large concentrations in the heart and liver with moderate amounts in skeletal muscle, kidneys, and pancreas.

GOT levels can be used to diagnose myocardial infarction within 10-48 hours. Other conditions with elevated GOT include arrhythmias and severe angina of the heart, and liver damage.