What Are Liver Function Tests?

What You Should Know About Your Blood Test

Liver function tests (LFTs), also referred to as hepatic function tests, a liver panel, or liver enzymes, are blood tests that measure several enzymes and proteins. These can include alkaline phosphatase (ALP), aspartate transaminase (AST), bilirubin, gamma-glutamyl transferase (GGT), and globulin, among several others. Values reflect how well your liver is functioning and are used to diagnose and monitor disease, infection, injury of the liver, among other concerns.

reasons to have a liver function test
 Illustration by Emily Roberts, Verywell

Purpose of Test

LFTs can be ordered as part of a routine annual physical. If you have an acute illness, you may also need to have LFTs as an outpatient or while you are in the hospital. Elevated or decreased concentration of liver enzymes provides your doctor with information that can be used to identify liver disease, and sometimes, to diagnose the type of liver disease.

You will need to have your LFTs checked if any of the following apply to you:

  • You take medications that can cause liver problems: Many prescriptions, over-the-counter medications, and herbal supplements can cause problems with liver function, including anti-depressants, cholesterol-lowering medications, Tylenol (acetaminophen), most nonsteroidal anti-inflammatories, vitamin A, and niacin. Generally, medications that can cause liver disease tend to do so if you are taking high amounts. But some people are more sensitive than others and may experience adverse effects on the liver even when these are taken at moderate doses.
  • You have symptoms of a gastrointestinal disease or liver disease: You are likely to have your LFTs checked if you have jaundice (yellow discoloration of the skin and eyes), abdominal pain, nausea, vomiting, abdominal swelling, dark-colored urine, unusual bleeding or bruising, excessive itching without a rash, unexplained weight loss, decreased appetite, or fatigue.
  • A liver imaging test result was abnormal: If you had an abdominal X-ray, ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scan for any reason, your doctor may have observed concerning features in the appearance of your liver that require follow-up with LFTs.
  • You engage in certain lifestyle choices: Heavy alcohol intake increases the risk of alcoholic liver disease, and IV drug use increases the risk of infectious hepatitis.
  • You have current or previous liver disease: If you have a history of hepatitis (liver inflammation), cancer of the liver, injury to your liver, a liver transplant, infectious hepatitis, or cirrhosis (end stage liver disease), you will need periodic follow-up to assess changes in your LFTs, which often reflect changes in your liver function.
  • You have certain other medical problems: Some chronic medical conditions, such as severe hypertension, lupus, diabetes, and colon cancer, can increase your chances of developing liver disease.

Limitations

LFTs can provide your doctors with information about your liver function, but these values do not provide diagnostic confirmation of the cause of your liver condition. The degree to which your LFTs differ from normal values does not necessarily correlate with the severity of your liver disease or indicate whether your illness is treatable. You can have mild blood test abnormalities with severe liver disease or significantly abnormal blood tests with mild, easily treatable disease.

In addition, changes in your LFT values may lag behind your liver disease. Your blood tests may not be abnormal if you have early liver disease and may not return to normal until months after your illness is treated.

Risks and Contraindications

Because LFTs are checked with a routine blood test, there are minimal risks and no contraindications. Some people with liver disease experience slow blood clotting, and it can take a few minutes longer than normal for the puncture site to stop bleeding, but there shouldn't be any serious bleeding or blood loss.

Before the Test

Liver function tests may be done as part of a doctor's office visit, if deemed necessary, or scheduled for a later date.

Timing

A blood test for LFTs should take a few minutes. If you are having it done during your medical appointment, it will only prolong your visit by a few minutes. If you have to go to a separate place or come back at a different time to have your blood drawn, you should be prepared to spend about half an hour in total because you will need to allow time to check in, sign routine forms, and wait your turn.

Location

If you don't have your blood drawn at your doctor's office, you may be sent to a lab or hospital where a phlebotomist is available. A phlebotomist is a healthcare professional trained to take blood samples.

What to Wear

You will have blood drawn from your arm or hand, so it is best to wear a short-sleeve or loose shirt so that you can easily roll up your sleeves.

Food and Drink

Your doctor may ask you to abstain from food and drink for six to eight hours before your blood test. If you have any questions be sure to ask at least a day prior to your blood draw so you don't accidentally eat or drink something that will change the results of the test.

Cost and Health Insurance

Your health insurance company may require a pre-authorization approval for this blood test. You may also be required to pay a co-pay, depending on your insurance coverage. If you are paying for the test out of pocket, the cost will range from between approximately $50 to several hundred dollars.

What to Bring to Your Blood Draw

You should bring your test order form (if applicable), your insurance card, a form of personal identification, and payment, if necessary.

During the Test

You will have your blood drawn by a nurse, a phlebotomist or someone else who has been trained to draw blood.

Pre-Test

When you check in, you will be asked to sign a consent form for the test and for payment, as well as a patient privacy form.

Throughout the Test

Your doctor may choose to test just a few enzymes or proteins, or many. Either way, the procedure—which should take just a few minutes—is the same.

You will be asked to sit in a chair, typically with an armrest. Your phlebotomist will ask you which hand you write with, as it is often preferable to have your blood drawn from your non-dominant arm.

You will be asked to expose your arm above your elbow. The phlebotomist will ask you to hold a fist and will apply a tourniquet around your arm, above your elbow. The skin on the inner surface of your arm will be cleaned and the needle inserted into a vein. You may feel a mildly sharp sensation when the needle is inserted, or it might not hurt at all. 

Your blood will be collected in a tube. Once done, the tourniquet and needle will be removed and gauze placed over the puncture site, which you will hold in place.

Post-Test

After a few seconds, your phlebotomist will check to see if the bleeding has stopped. If so, a bandage will be placed over the small puncture wound. 

If your bleeding does not stop within a minute, you will be asked to firmly hold down gauze on the wound for a few more minutes until your phlebotomist verifies that the bleeding has stopped.

After the Test

After this, you should be free to leave. If you have been fasting, it is a good idea to get something to eat and drink so that you don't feel dizzy. You can drive and resume your normal activities after having your LFTs checked. 

Managing Side Effects

If you have liver disease and your wound continues to bleed, or if the puncture site becomes swollen, feels warm to the touch, or becomes black and blue, tell your doctor.

Interpreting Results

Your liver function test results will reflect levels of the different enzymes and proteins that your doctor specifically ordered be checked.

The individual test results are typically used together, not individually, to diagnose a liver problem. For example, if one number is mildly elevated, it likely won't cause concern. 

While LFTs are typically used to detect liver problems, the heart can also release AST, so your doctor will consider the entire set of liver tests, rather than just this one test, when making a diagnosis. LFT results can also be abnormal due to the effect conditions such as severe blood loss, systemic illness, and malnutrition have on the liver.

Alanine Aminotransferase (ALT)

This test is used to detect liver injuries and long-term liver disease. Highly elevated levels may indicate active hepatitis from any cause, including a virus, alcohol, a drug, or a toxin. Some prescription and over-the-counter medications can cause an increase in ALT levels as well.

ALT levels can be dramatically affected by severe blood loss, low blood pressure, or any condition that deprives the liver of blood and oxygen. For this reason, you or a loved one may have an elevated ALT with a severe medical illness that requires care in the intensive care area of the hospital.

Normal level: 5 to 40 units/liter

Albumin

Albumin is a protein made by the liver. If the liver has chronic or acute damage, the level of albumin in the blood will typically be low. A low level of albumin can also be caused by poor nutrition and can develop due to malnutrition or chronic illness.

Normal level: 3.5 to 5 grams/100 ml

Alkaline Phosphatase (Alk Phos, ALP)

ALP is a substance found in the bile ducts of the liver. An elevation in ALP doesn't necessarily mean that the liver itself is having the problem, but can be an indication that the ducts that leave the liver may be obstructed or diseased.

Normal level: 13 to 39 units/liter

Asparate Phosphatase (AST)

AST levels can be elevated if you have severe blood loss, low blood pressure, or any condition that deprives the liver of blood and oxygen.

Normal level: Male: 8 to 46 units/liter, Female: 7 to 34 units/liter

Bilirubin

Your results may include three different bilirubin levels:

  • Total bilirubin (T. Bili): This lab test measures the total amount of bilirubin in the blood (direct and indirect). Bilirubin is produced during normal blood cell breakdown and is excreted by the liver through bile. Liver dysfunction results in a build-up of bilirubin in the blood. Bilirubin is yellow, so high levels may be suspected even before testing if your skin or the whites of your eyes take on this color (jaundice). However, total bilirubin levels may be elevated before jaundice becomes visibly apparent.
    Normal level: 0.3 to 1.9 mg/100 ml
  • Indirect bilirubin (I. Bili): Indirect bilirubin does not dissolve in water. In order to be properly eliminated from the body, it must go to the liver where it is made into direct (water-soluble) bilirubin.
    Indirect Bilirubin = Total Bilirubin–Direct Bilirubin
    Normal level: 0.1 to 1.0 mg/100 ml
  • Direct Bilirubin (D. Bili): Direct bilirubin is produced when the indirect type is converted into a water-soluble form by the liver. The proportion of indirect to direct bilirubin may change if the liver has difficulty with this task.
    Normal level: less than 0.4 mg/100 ml

    Gamma-Glutamyl Transferase (GGT)

    GTT can be elevated in early liver disease, making it a highly sensitive marker. But it is not specific and can be elevated with a variety of liver diseases, as well as with congestive heart failure. It can also be elevated after heavy alcohol use.

    Normal level: 9 to 48 units/liter

    Globulin

    Globulin is an immunologic protein produced in the liver. Low globulin levels are a non-specific sign of liver dysfunction.

    Normal level: 2 to 35 grams/liter

    Prothrombin Time (PT)

    Prothrombin is a protein involved in blood clotting, and prothrombin time is a measure of how long it takes your blood to clot. Prolonged PT can be a sign of liver disease.

    Normal: 11 to 14 seconds

    Follow-Up

    If your LFTs are not normal, you may need additional blood tests to determine the cause, such as tests for infectious hepatitis or inflammatory disease. You may also need to have imaging tests so that your doctors can visualize your liver. If there is a chance that you could have cancer in your liver, you will likely also need a biopsy.

    You may also need to have follow-up LFTs at some point. For example, if you have an alcoholic liver disease, you may need to have follow-up tests in six months to see if your numbers have improved after stopping drinking (or worsened after having continued).

    If you have had bile duct obstruction, you may need interventional treatment or surgery, and you should expect to have your tests repeated within a few weeks to monitor your liver function.

    If you have a severe systemic disease, you may need your liver enzymes regularly followed every week or so while you are recovering.

    A Word From Verywell

    There are a number of reasons to have your liver function tests checked. The blood test itself is uncomplicated and simple. Evaluation and treatment of liver disease is complex, encompassing a variety of vastly different condition possibilities that range in severity, are treated differently, and have different prognoses.

    If you need to have LFTs checked for a chronic condition, it is a good idea to save your test results in the event you change doctors or hospitals. A complete record can provide your care team with critical information that can help them track your disease over time.

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