All you need to know about ALT (Alanine Aminotransferase) Test

A prescription from the doctor to the patient to make ALT Test


Alanine aminotransferase or ALT is an enzyme made by cells in the liver. It is mostly found in the cells of the kidney and liver but small amounts can also be found in the muscles and in the heart.  An ALT test is used to measure ALT levels in the blood to screen for liver damage and to help diagnose liver diseases. ALT test is also known as serum glutamic-pyruvic transaminase or SGPT test.

The liver is the largest gland in the body located in the upper right hand of the abdominals, just beneath the rib cage. It has various essential functions such as processing the nutrients of the body, producing important proteins like albumin and blood clotting factors, storing iron and vitamins, breaking down potentially toxic substances from the blood, and producing bile that helps in digestion.

Enzymes, a form of protein, assist the liver in breaking down other proteins in order for the body to easily absorb these proteins. ALT is one of the enzymes that play a very important role in metabolism.

Importance of ALT

ALT functions by converting alanine, an amino acid that can be found in proteins, into pyruvate, an essential intermediate in the production of cellular energy. ALT levels are low in healthy individuals. ALT is released into the bloodstream when the liver is damaged. It usually happens before the signs and symptoms of liver damage appear. When it occurs, the serum ALT levels rise.

ALT is a very useful test in the early detection of liver damage that’s why it is frequently a part of the initial screening for liver diseases. Measuring the ALT levels in an individual’s blood helps the doctors assess liver function or conclude the underlying cause or condition of a liver problem.

There are several conditions that can cause liver damage which results in increased ALT levels. Cirrhosis and hepatitis are examples of these diseases.

Factors that prompt an ALT test

ALT test can be recommended during a routine health examination as part of a comprehensive metabolic panel. The doctor also usually recommends an ALT test when an individual shows signs and symptoms of liver problems like:

  • Fatigue or extreme tiredness
  • Loss of appetite
  • Nausea and Vomiting
  • Weakness
  • Stomach pain or swelling
  • Jaundice or yellowing of the skin or eyes
  • Abdominal pain
  • Dark urine
  • Itchy skin
  • Light-colored stool

An ALT test may also be ordered by the doctor along with other tests to individuals who are at a higher risk for liver diseases because there are a lot of people with mild liver damage who don’t experience any signs or symptoms. ALT levels are increased even with mild liver damage. Here are some of the risk factors for liver damage:

  • Alcohol bingeing
  • Family history of liver diseases
  • History or exposure to hepatitis viruses
  • Intake of medicines that are known to cause liver damage
  • Overweight
  • Diabetes

ALT test may be performed to:

  • Monitor progression and treatment of individuals who have a liver disease
  • Assess whether the treatment should be started
  • Evaluate how the treatment is working and determine whether the therapy is effective

How ALT test is performed

ALT test is done by drawing a blood sample usually from a vein in the arm.

  1. A nurse or a lab tech clean the skin in the area where they will insert a needle through an antiseptic.
  2. The nurse or lab tech ties an elastic band around the upper arm to stop the blood flow and allow the veins in the arm to be more visible.
  3. Once he/she is able to locate a vein, he/she inserts a needle into it which can cause a slight stinging sensation just like ant bites. The blood is collected into a tube that is connected at needle’s end.
  4. When an ample amount blood has been drawn, the nurse or lab tech removes the needle and then the elastic band. He/she puts a small piece of gauze or cotton over the area where the needle was inserted and put tape or bandage on top of it to keep it in intact.
  5. He/she sends the extracted blood sample to the laboratory for analysis.
  6. The laboratory personnel sends the results to the doctor.
  7. The doctor schedules an appointment to discuss the results of the test.

What ALT test results mean

Normal Results

A low level of ALT is normal and is expected. 7 to 55 units per Liter is the normal value for ALT in the blood but the value can be different depending on the hospital. The range may be influenced by some factors such as age and gender.

Abnormal Results

ALT levels that are higher than the normal levels indicate a liver disease. Elevated ALT levels may be caused by the following:

ALT is often done together with AST or aspartate aminotransferase as part of a comprehensive metabolic panel or liver panel to screen and diagnose liver diseases. The ALT level is higher than AST in many cases of liver diseases and the AST/ALT ratio is usually less than 1.