In general, liver blood tests are used to detect an injury or an inflammation to the liver. These tests are commonly ordered and performed in many situations, such as in routine health screening, evaluation of abdominal pain, or suspectedliver disease.
The liver blood tests are typically done as a part of the comprehensive metabolic panel which also includes electrolyte levels and kidney function.
The main values measured in liver blood tests are the aminotransferases (alanine aminotransferase or ALT and aspartate aminotransferase or AST).
The other measurements include alkaline phosphatase, albumin, and bilirubin.
It is important to note that these tests are commonly referred to as “liver function tests”, but this term is misleading as the aminotransferases and alkaline phosphatase do not reflect the function of the liver.
Strictly speaking, the true liver function tests (LFT’s) include albumin, bilirubin, blood coagulation panel, and glucose.
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) and they will be covered in this article.
What are common liver blood tests?
Liver blood tests are some of the most commonly performed blood tests. These tests can be used to assess liver functions or liver injury.
An initial step in detecting liver damage is a simple blood test to determine the level of certain liver enzymes (proteins) in the blood.
Under normal circumstances, these enzymes mostly reside within the cells of the liver. But when the liver is injured for any reason, these enzymes are spilled into the blood stream.
Enzymes are proteins that are present throughout the body, each with a unique function.
Enzymes help to speed up (catalyze) routine and vital chemical reactions in the body.
Among the most sensitive and widely used liver enzymes are the aminotransferases. They include aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT).
These enzymes are normally predominantly contained within liver cells and to a lesser degree in the muscle cells.
If the liver is injured or damaged, the liver cells spill these enzymes into the blood, raising the AST and ALT enzyme blood levels and signaling liver disease.
Other blood tests pertaining to the liver are measurements of some of the other enzymes found the liver.
In addition to AST and ALT, alkaline phosphatase, 5′ nucleotidase, and gamma-glutamyl transpeptidase (GGT) are a few of the other enzymes located in the liver.
The focus of this article is mainly on the most common liver enzymes, AST and 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 (SGPT).
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.
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)
What are some common reasons for abnormal liver tests?
Abnormal liver tests may be detected in the blood in a variety of liver conditions.
Mild to moderate elevations of the liver enzymes are common. They are often unexpectedly encountered on routine blood screening tests in otherwise healthy individuals.
The AST and ALT readings in such cases are usually between twice the upper limits of normal and several hundred units/liter.
One of the most common causes of mild to moderate elevations of these liver tests is a condition referred to as fatty liver (steatohepatitis or hepatic steatosis). In the United States, the most frequent cause of fatty liver is alcohol abuse. Other causes of fatty liver include diabetes mellitus and obesity.
Chronic hepatitis B and hepatitis C are other causes of chronic mild to moderate liver enzyme elevation.
In these conditions, ALT and AST may be only slightly high and the degree of abnormality in liver function tests can indicate the degree if injury.
Chronic and acute alcohol use also can commonly cause abnormal liver blood tests. In alcoholic hepatitis, the range of liver tests can vary greatly.
In chronic alcohol liver disease or alcoholic cirrhosis, slight elevation of ALT and AST may be observed, whereas in acute alcoholic hepatitis, high liver enzyme numbers are often seen.
Many medications can be responsible for mild to moderate increase in the liver enzyme tests
What medications can cause increased liver enzyme tests (abnormal aminotransferase levels)?
A variety of medications can cause abnormal liver enzymes levels in some individuals.
Examples of some of the common medications with potential liver toxicity include:
Pain relief medications such as:
- acetaminophen (Tylenol),
- ibuprofen (Advil, Motrin),
- naproxen (Naprosyn, Naprelan, Anaprox, Aleve),
- diclofenac (Voltaren, Cataflam, Voltaren-XR), and
- phenylbutazone (Butazolidine)
Anti-seizure medications such as:
- phenytoin (Dilantin),
- valproic acid (Depakote, Depakote ER, Depakene, Depacon),
- carbamazepine (Tegretol, Tegretol XR, Equertro), and
Antibiotics such as:
- tetracyclines, (for example, tetracycline [Achromycin])
- isoniazid (INH) (Nydrazid, Laniazid)
- sulfamethoxazole (Gantanol),
- trimethoprim (Trimpex; Proloprim, Primsol)
- nitrofurantoin (Macrodantin; Furadantin; Macrobid),
- fluconazole (Diflucan ) and some other anti-fungals, etc.
Cholesterol lowering drugs such as statins:
- lovastatin (Mevacor, Altocor),
- pravastatin (Pravachol),
- atorvastatin (Lipitor),
- fluvastatin (Lescol),
- simvastatin (Zocor),
- rosuvastatin (Crestor), and
Cardiovascular drugs such as:
- amiodarone (Cordarone),
- hydralazine (Apresoline)
- quinidine (Quinaglute, Quinidex), etc.
Antidepressant drugs of the tricyclic type
With drug-induced liver enzyme abnormalities, the enzymes usually normalize weeks to months after stopping the medications.
What conditions can cause very high aminotransferase levels?
AST and ALT serum levels in some liver conditions can range anywhere from ten times the upper limits of normal to thousands of units/liter The highest levels of AST and ALT are found with disorders that cause rapid death of numerous liver cells (extensive hepatic necrosis).
Although this degree of liver enzymes elevation is not common, it can occur in such conditions as:
- Acute viral hepatitis A or B
- Profound liver damage inflicted by toxins as from an overdose of acetaminophen (brand-name Tylenol) or mushroom poisoning
- Prolonged collapse of the circulatory system (shock) when the liver is deprived of fresh blood providing oxygen and nutrients
Also, very high AST and ALT levels can be a result of severe muscle diseases.
What are some of the less common causes of elevated liver blood tests?
Less common causes of abnormal liver enzymes in the United States include hemachromatosis (iron overload), Wilson’s disease, alpha-1-antitrypsin deficiency, celiac disease, Crohn’s disease, ulcerative colitis, and autoimmune hepatitis.
Though not as common as hepatitis C, hepatitis B can cause chronic liver disease with persistently abnormal liver enzymes.
Hemachromatosis is a genetic (inherited) disorder in which there is excessive absorption of dietary iron leading to accumulation of iron in the liver with resultant inflammation and scarring of the liver.
If undiagnosed or untreated, hemachromatosis can progress to cirrhosis and liver failure.
Wilson’s disease is an inherited disorder with excessive accumulation of copper in diverse tissues including the liver and the brain.
Excess copper in the liver can lead to chronic liver inflammation, while copper in the brain can cause psychiatric and motor disturbances.
Alpha-1-antitrypsin deficiency is an inherited disorder in which the lack of a glycoprotein (carbohydrate-protein complex) called alpha-1-antitrypsin lead to chronic lung disease (emphysema) and chronic liver disease.
Autoimmune hepatitis results from liver injury brought about by the body’s own antibodies and defense systems attacking the liver.
Celiac disease (celiac sprue) is a disease of the small intestine where a person has an allergy to gluten and develops gas, bloating, diarrhea, and in advanced cases malnutrition.
Patients’ with celiac dksease can also develop mildly abnormal ALT and AST levels.
Crohn’s disease and ulcerative colitis are diseases with chronic inflammation of the intestines (collectively referred to as inflammatory bowel diseases).
In these individuals inflammation of the liver (hepatitis) or bile ducts (primary sclerosing cholangitis) also can occur, causing abnormal liver tests.
Viral infections other than common hepatitis viruses (A, B, C) can sometimes cause elevation of liver enzymes as they can result in generalized body infection and liver inflammation.
Non-viral infections of the liver are rare, but they can cause liver damage.
Bacterial and amebic hepatic (liver) abscesses typically present as focal infection and inflammation of the liver as opposed to viral hepatitis where generalized liver inflammation occurs.
Liver enzyme elevation is usually seen in the setting of these infections.
Rarely, abnormal liver enzymes can be a sign of liver cancer. Cancer arising from liver cells is called hepatocellular carcinoma or hepatoma.
Cancers spreading to the liver from other organs (such as colon, pancreas, stomach, and others) are called metastatic malignancies (to the liver).
Liver hemangiomas (masses of abnormal and atypical blood vessels within the liver) are the most common tumors in the liver.
Hepatic hemangiomas are benign and in general do not cause elevation of liver tests.
Another rare condition that causes elevation of liver tests is called the Budd-Chiari Syndrome.In this condition, obstruction of blood flow in the liver by a blood clot can damage the liver by limiting blood flow leading to injury of liver cells.
As a result of this insult, liver enzymes may rise indicating hepatic inflammation.
Glycogen storage disorders are genetic conditions seen in pediatric population (detected at birth in severe types or later in childhood in less severe types).
They impair the ability of liver to store and metabolize glycogen, a complex sugar necessary for production of nutrients and energy in the body.
Glycogen storage disorders cause varying degrees of liver enzyme abnormalities.
Monitoring Aminotransferase 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.