Liver Blood Tests

Reviewed on 7/23/2022

What Are Liver Blood Tests Used For?

Picture of Liver Function Test
Liver blood tests are used to find liver abnormalities, such as inflammation, liver damage, or liver disease. Photo by iStock

Liver blood tests are designed to show evidence that abnormalities, for example, inflammation, liver cell damage, has or is occurring within the liver.

The blood tests most frequently used for liver disease are the aminotransferases (alanine aminotransferase or ALT and aspartate aminotransferase or AST).

People with mild to moderate elevations of AST and ALT may have no symptoms or mild systemic symptoms. These may include

What Are Normal and Elevated (High) Levels of Liver Enzymes?

Understand AST and ALT levels
Common causes of elevated ALT and AST are viral liver infections, alcohol abuse, cirrhosis (from any chronic causes), and more.
  • Normal levels of ALT (SGPT) ranges from about 7-56 units/liter of serum (the liquid part of the blood),
  • Normal levels of AST (SGOT) is about 5-40 units/liter of serum.
  • Elevated levels of AST and ALT may signify the level of liver damage in a person. The interpretation of elevated AST and ALT results depends upon the entire clinical evaluation of an individual, and so it is best done by physicians experienced in evaluating liver disease and muscle disease.

What Diseases and Drugs Cause Elevated Liver Enzymes?

Common causes of elevated ALT and AST are

Common causes of abnormal AST and ALT levels are wide-ranging (for example, toxins, and autoimmune diseases).

Many drugs may cause elevated blood levels of AST, and ALT and some medications can cause severe damage, for example, acetaminophen (Tylenol).

What Are AST and ALT (Aminotransferases)?

Aminotransferases are enzymes (proteins that help speed up chemical reactions in the body) that are found mainly in the liver, but also in other tissues, such as muscles. They are a part of the normal metabolic processes in the liver and are responsible for transferring amino acids (components that build proteins) from one molecule to another. ALT was formerly known as serum glutamic-pyruvic transaminase (SGPT) and AST as serum glutamic-oxaloacetic transaminase (SGOT).

What Are the Symptoms of Abnormal Levels of Liver Enzymes?

Symptoms of mild to moderate elevation of liver enzymes may vary from no symptoms at all too generalized symptoms that include

Mild to moderate elevations of the liver enzymes are common. They are often unexpectedly encountered on routine blood screening tests in otherwise healthy individuals. 

What Are Normal and Elevated (High) Levels of AST and ALT?

What Are Normal Levels of AST and ALT?

Normal levels of AST and ALT may slightly vary depending on the individual laboratory's reference values.

  • Typically the range for normal AST is reported between 10 to 40 units per liter and ALT between 7 to 56 units per liter.
  • Mild elevations are generally considered to be 2-3 times higher than the normal range.
  • In some conditions, these enzymes can be severely elevated, in the 1000s range.

What Are Elevated (High) Levels of AST and ALT?

Elevated levels of liver enzymes in general signify some form of liver (or hepatic) damage or injury.

  • These levels may be elevated acutely (short term) indicating sudden injury to the liver, or they may be elevated chronically (long term) suggesting ongoing liver injury.
  • In addition to the duration, the level of abnormal elevation of the aminotransferases is also significant.
  • In some conditions the elevation could be mild, consistent with a mild injury or inflammation of the liver.
  • They can also be severely elevated, possibly up to 10 to 20 times the normal values, suggesting more significant damage to the liver.

Diseases That Cause Elevated Liver Enzymes in the Blood

Fatty liver disease
One of the most common causes of mild to moderate elevations of these liver tests is a condition referred to as fatty liver. Source: iStock

The most common diseases causing abnormally elevated ALT and AST are acute viral hepatitis, such as

  • hepatitis A or B,
  • chronic viral hepatitis,
  • such as hepatitis B or C,
  • cirrhosis of the liver (scarring of the liver due to long-standing inflammation of the liver),
  • liver damage from alcohol abuse or alcoholic fatty liver,
  • hemochromatosis (a genetic condition causing long-standing liver damage due to iron build up in the liver), and
  • diminished blood flow to the liver (from shock or heart failure).

Medications That Cause Abnormal Levels of Liver Enzymes in the Blood

The common medications with potential liver toxicity include pain relief medications. Source: iStock

What Are Less Common Causes of Abnormal Liver Enzymes?

There are many other causes of the abnormally elevated blood liver enzyme levels in addition to those mentioned above. Some of these conditions include:

What Tests and Procedures Diagnose the Causes of Abnormal Levels of Liver Enzymes?

The most important step in evaluating patients with abnormal liver enzyme levels is to take a thorough medical history and perform a complete medical examination. All the patient's medications, including over-the-counter drugs (OTC, and herbal remedies.

  • Any history of blood transfusion (especially if done a long time ago when screening for donated blood was much less strict), history of intravenous (injection) or intranasal (snorting) drug use or needle sharing, tattoos, sexual contact with someone with possible viral hepatitis, alcohol consumption, foreign travel, and possible consumption of contaminated food need to be questioned.
  • Moreover, in addition to the liver tests (transaminases), other tests to screen the liver functions, such as a blood coagulation panel, albumin level, and total bilirubin level as well as a complete blood count need to be measured.
  • Screening for viral hepatitis is also routinely done to detect any possible active infections of the liver (acute or chronic active) or to determine immunity against these viruses either through prior infections or vaccination.

In many instances, a doctor may also order an ultrasound of the liver to assess the structure of the liver and the biliary tree as well to look for any gallstones that may be causing the liver disease.

Monitoring Abnormal Levels of Enzymes in the Blood

Liver tests are monitored depending on the degree, the duration, and cause of the abnormality. For example, in a person who has chronic (long standing) hepatitis B or C infection, the liver specialist (hepatologist) may opt for surveillance of these levels every 3 to 6 months to ensure that they are not rising.

On the other hand, if a healthy person is seen in the hospital for Tylenol overdose, then he or she needs to be monitored very closely, and ALT and ALT levels may be drawn a few times a day to monitor their trend and to guide therapy.

Other Liver Blood Tests That Measure Abnormal Levels of Enzymes in the Blood

There are several other liver enzymes performing important functions, however, many of these are not routinely measures in blood tests.

  • Alkaline phosphatase is very commonly reported with the transaminases as part of the metabolic panel blood test. This molecule typically resides in the wall of the intra- and extra-biliary ducts (tube-like structures within the liver that connect liver cells together and ultimately coalesce to from the bile duct, connecting the liver to the gallbladder).
  • The elevation of this enzyme may indicate and injury or an inflammation to these tubes (ducts). Common causes for this are gallbladder obstruction and certain medications.

There also are other liver enzymes such as, lactate dehydrogenase (LDH), glutamate dehydrogenase, and gamma-glutamyltranspeptidase (GGT), which are less routinely measured clinically.

How Long Will It Take to Get the Results (Interpretation) of Your Liver Blood Tests?

The ALT and AST levels are obtained directly from a blood sample that is sent to the laboratory for measurement. The results are usually available within hours to days and are reported to the ordering doctor for review.

Reviewed on 7/23/2022
REFERENCE: Diagnosing Liver Disease - Liver Biopsy and Liver Function Tests. American Liver Foundation.