Liver Blood Tests

Facts and Definition of Liver Blood Test

  • 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).
  • Normal levels of ALT ranges from about 7-56 units/liter, and 10-40units/liters for AST.
  • Elevated levels of AST and ALT may signify the level of liver damage in a person.
  • Common causes of elevated ALT and AST are
  • Many drugs may cause elevated AST, and ALT and some medications can cause severe damage (for example, acetaminophen [Tylenol liver damage]).
  • Less common causes of abnormal AST and ALT levels are wide ranging (for example, toxins, and autoimmune diseases)
  • People with mild to moderate elevations of AST and ALT with no or few symptoms should follow-up with their doctor for potential underlying causes of elevated AST and/or ALT.
  • Repeated test levels (monitoring) is useful in some patients (for example, viral-caused and Tylenol-caused elevations) to guide therapeutic treatments.
  • Other liver enzymes, although not measured routinely, may add additional information about liver functions.

Aminotransferases (AST, ALT)

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).

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.

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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.

Elevated 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 Abnormal Aminotransferase Levels

The most common diseases causing abnormally elevated ALT and AST are:

  • Acute viral hepatitis, such as hepatitis A or B
  • Chronic viral hepatitis, such 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)
  • Diminished blood flow to the liver (from shock or heart failure)

Medications That Cause Abnormal Aminotransferase Levels

Less Common Causes of Abnormal Aminotransferase Levels

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

Evaluation of Healthy Patients for Mild to Moderate Rises in Aminotransferase Levels

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 and herbal remedies need to be noted.

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.

Furthermore, 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 physician 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.

Symptoms of the mild to moderate elevation of liver enzymes may vary from no symptoms at all to generalized:

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Monitoring ALS and ALT Levels

Monitoring of the liver tests depends on the degree, the duration, and the 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 Enzymes

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

Reviewed on 9/11/2017

REFERENCE: American Liver Foundation. Liver Function Tests. Jan14,2015.

Medically reviewed by Martin E Zipser, MD; American board of Surgery

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