AST (SGOT) Test: Meaning, Normal Range, High & Low Levels, Causes, Symptoms, and Complete Medical Guide
What Is AST (SGOT)?
AST stands for Aspartate Aminotransferase, and it is also known as SGOT (Serum Glutamic-Oxaloacetic Transaminase). It is an enzyme naturally present inside many organs of the body. The liver contains the highest amount of AST, but it is also found in the heart, muscles, kidneys, pancreas, and even red blood cells.
The AST test measures the level of this enzyme in your blood. When cells in these organs become injured or inflamed, AST leaks into the bloodstream. This is why high AST levels are often a sign of liver injury, muscle damage, or, in some cases, heart problems.
Doctors often test AST along with ALT (SGPT) because using both values gives a more accurate picture of liver health.
Where Is AST Produced in the Body?
AST is made inside the cells of several organs. Although the liver is the most common source, the enzyme exists in many tissues, which is why elevated AST does not always point only to liver disease.
Organs and Tissues That Produce AST
- Liver (hepatocytes): The main source of AST in the body
- Heart muscles: Levels rise dramatically during a heart attack
- Skeletal muscles: Increases after injury, vigorous exercise, or muscle disease
- Kidneys and pancreas: Mild increases seen during inflammation
- Brain: Elevated during severe brain injury or stroke
- Red blood cells: Hemolysis (RBC destruction) releases AST
Because AST is spread across multiple organs, doctors analyze its levels along with other tests—especially ALT—to determine the exact source of the problem.
Main Functions and Importance of AST
AST is an enzyme, meaning it helps speed up chemical reactions in the body. Its primary role is related to metabolism, but its clinical importance is mainly due to its value as a diagnostic marker.
Helps in Protein Metabolism
AST helps convert amino acids into energy-producing molecules inside cells. Although this is an internal cellular function, measuring AST helps detect cell damage.
Supports Energy Production
AST is part of the Krebs cycle, a major process that helps cells generate energy.
Marker for Liver Health
Because liver cells contain large amounts of AST, high levels often point to liver injury, inflammation, or disease.
Detects Muscle and Heart Problems
Muscle breakdown (due to exercise, trauma, or disorders) and heart attacks can raise AST significantly.
AST/ALT Ratio for Diagnosis
Doctors check the ratio between AST and ALT:
- AST > ALT: Often suggests alcohol-related liver disease
- ALT > AST: More common in viral hepatitis or fatty liver disease
This ratio helps pinpoint the exact liver condition.
Causes of Low AST Levels
Low AST levels are usually not a cause for concern. In most cases, they are considered normal or related to harmless variations in metabolism.
Common Causes
- Vitamin B6 deficiency: This vitamin is required for AST activity
- End-stage liver failure: Very few functioning liver cells left to produce AST
- Normal physiological variation: Some people naturally have low levels
Low AST rarely requires treatment unless accompanied by symptoms of severe liver disease.
Symptoms of Low AST
Low AST itself does not cause symptoms. If it is low due to liver failure, symptoms may include:
- Extreme tiredness
- Pale skin
- Loss of appetite
- Severe weakness
- Swelling in the abdomen (late-stage liver disease)
However, low AST on its own is generally harmless.
Causes of High AST Levels
High AST is much more common than low levels. It indicates cell damage in one or more organ systems.
Liver-Related Causes
Hepatitis
Inflammation of the liver from viruses, alcohol, autoimmune diseases, or toxins.
Fatty Liver Disease
Both alcoholic and non-alcoholic fatty liver can elevate AST.
Cirrhosis
Long-term liver damage results in scarring, raising liver enzyme levels.
Alcohol-Related Liver Injury
Heavy or chronic alcohol use typically causes AST to rise more than ALT.
Non-Liver Causes
Heart Attack
When heart muscle is damaged, AST rises rapidly.
Muscle Injury or Heavy Exercise
Intense workouts, accidents, or muscle diseases (myopathies) can raise AST significantly.
Pancreatitis
Inflammation of the pancreas often elevates liver enzymes.
Hemolysis
Breakdown of red blood cells releases AST into the bloodstream.
Medications
Some drugs can irritate the liver or muscles, raising AST levels:
- Statins
- Certain antibiotics
- Anti-seizure medicines
- Painkillers
- Alcohol-containing medications
Symptoms of High AST
AST does not create its own symptoms. Instead, symptoms come from the underlying condition causing the increase.
Liver-Related Symptoms
- Yellowing of eyes and skin (jaundice)
- Dark-colored urine
- Pale stools
- Right-sided abdominal pain
- Loss of appetite
- Persistent fatigue
Heart-Related Symptoms (Possible Heart Attack)
- Chest pain
- Shortness of breath
- Sweating
- Pain radiating to the arm, shoulder, or jaw
Muscle-Related Symptoms
- Muscle pain or soreness
- Weakness
- Swelling of muscles
- Stiffness after exercise
If AST is high along with ALT, GGT, or ALP, the liver is the most likely source.
AST Reference Range
Reference ranges may vary between laboratories, but typical values include:
- Normal AST Level: 5 – 40 U/L
AST/ALT Ratio
Doctors use this ratio to understand the cause:
- AST > ALT: Suggests alcoholic liver disease or muscle injury
- ALT > AST: Indicates hepatitis, fatty liver, or viral inflammation
This ratio is an important diagnostic tool.
Sample Type and Collection
- Sample Type: Serum
- Tube Used: Red top (plain tube)
A sample of blood is taken from a vein and tested for enzyme levels.
Test Preparation
AST testing is generally simple. Most people do not need special preparation.
Fasting
- Usually not required, unless advised by the doctor.
Medication Check
- Some medications raise AST. Always inform your doctor if you take:
- Statins
- Antibiotics
- Anti-seizure drugs
- Pain medications
- Herbal supplements
Avoid Heavy Exercise
Intense workouts can temporarily increase AST levels, leading to misleading results. Avoid heavy exercise 24 hours before the test.
Alcohol
Avoid alcohol before the test, as it raises AST.
When to Consult a Doctor
You should speak with a doctor if:
- Your AST levels remain high in repeated tests
- You develop jaundice, dark urine, or pale stools
- You experience unexplained fatigue or weakness
- You have muscle pain or severe soreness after normal activity
- You use alcohol regularly and your AST is elevated
- Your AST/ALT ratio is abnormal
Early evaluation can help detect liver disease, heart conditions, or muscle problems before they worsen.
Important Medical Word Explanations
- Enzyme: A protein that speeds up chemical reactions in the body.
- Hepatitis: Inflammation or infection of the liver.
- Cirrhosis: Long-term liver damage causing permanent scarring.
- Haemolysis: Destruction of red blood cells.
- SGOT: Another name for AST.
- Myopathy: Diseases that affect muscle tissue.
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