These can include alkaline phosphatase (ALP), aspartate transaminase (AST), bilirubin, and gamma-glutamyl transferase (GGT), among others. Values reflect how well your liver is functioning and are used to diagnose and monitor disease, infection, and liver injury.
This article explains the purpose of liver function tests and their limitations. It also describes how to prepare for the test beforehand, what to expect while it takes place, and what happens afterward.
Reasons to Get a Liver Function Test
LFTs can be ordered as part of a routine annual physical. If you have a short-term (acute) illness, you may also need to have LFTs as an outpatient or while you’re in the hospital.
Elevated or decreased concentration of liver enzymes provides your healthcare provider with information that can be used to identify liver disease and, sometimes, diagnose the type of liver disease.
The tests can also be helpful when the following needs or circumstances arise.
Medication Side Effects
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 taken in large quantities.
Sometimes, appearances can be deceiving. For example, the American College of Gastroenterology notes that even herbs and supplements touted as “natural” can end up being “toxic to the liver.” However, the college stops short of saying what constitutes a toxic intake.
Symptoms of Gastrointestinal or Liver Disease
You are likely to have your liver function checked if you have symptoms of gastrointestinal or liver disease, such as:
Jaundice (yellow discoloration of the skin and eyes)Abdominal painNausea, vomitingAbdominal swellingDark-colored urineUnusual bleeding or bruisingExcessive itching without a rashUnexplained weight lossDecreased appetiteFatigue
Follow-Up to Liver Imaging Test
If you had an abdominal X-ray, ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scan for any reason, your healthcare provider may have observed concerning features in the appearance of your liver.
LFTs may be performed as a follow-up to learn more about your condition and why your imaging results were abnormal.
Screening in High-Risk People
Some chronic medical conditions, such as severe hypertension, lupus, diabetes, and colon cancer, can increase your chances of developing liver disease.
Certain lifestyle factors can play into the risk of liver injury as well. Heavy alcohol intake increases the risk of alcoholic liver disease, and IV drug use increases the risk of infectious hepatitis.
Ongoing Monitoring of 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-ups to assess changes in your liver function.
LFTs often reflect changes in liver function that must be monitored over time.
Risks and Contraindications
Because liver function is checked with a routine blood test, there are minimal risks and no contraindications.
There are some limitations of liver function tests. LFTs can provide your healthcare provider with information about your liver function, but these values do not confirm the cause of your liver condition.
Additionally, though the degree to which your LFTs differ from normal values usually indicates the severity of your liver disease, this is not always the case. In other words, you can have mild blood test abnormalities with severe liver disease or significantly abnormal blood tests with mild, easily treatable disease.
Changes in your LFT values may lag behind your liver disease as well. 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.
What to Expect
Liver function tests may be done as part of a healthcare provider’s office visit, if deemed necessary, or scheduled for a later date.
Before
You may have your blood drawn at your healthcare provider’s office. If not, you may be sent to a lab or hospital to have it done. Make sure you get there early enough to check in, fill out forms, and pay for the tests (if applicable).
You may need to abstain from food and drink for six to eight hours before your blood test. You may also have to stop certain medications in advance of the test. If you have any questions about restrictions, be sure to ask well in advance of your test so you don’t accidentally do something that can affect the test results.
You will have blood drawn from your arm or hand, so it is best to wear a short-sleeve or one with sleeves that can easily be rolled up.
During
You will have your blood drawn by a nurse, a phlebotomist, or someone else trained to draw blood. The test itself should take only a few minutes.
You’ll be asked to expose your arm above the elbow and make a fist. A tourniquet will then be tied 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.
After
Once the blood is drawn, the practitioner will stop the bleeding with gauze or a cotton ball and then bandage the site.
After this, you should be free to leave. If you’ve been fasting, it’s a good idea to eat or drink something right away. As long as you feel okay, you should be able to drive yourself from the facility and resume your normal activities.
Interpreting Results
Your liver function test results will reflect levels of the different enzymes and proteins that your healthcare provider specifically asked to be checked.
Do not attempt to treat these issues on your own. Get medical help.
The individual test results are typically used together, not individually, to diagnose a liver problem. So for example, if one number is slightly elevated, it likely won’t be cause for concern. It’s when several results are abnormal that a problem may be suspected.
Alanine Aminotransferase (ALT, SGPT) Aspartate Phosphatase (AST, SGOT)
These tests measure levels of enzymes that are released from damaged liver cells. Anything that injures the liver—whether it’s a medication, virus, or something else—can lead to high levels of these enzymes. The same goes for anything that decreases the flow of oxygen or blood to the liver.
High levels are anything above these normal values:
ALT: 8 to 37 units/literAST: 10 to 34 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 below the normal range of 3.9 to 5 grams/100 ml.
A low level of albumin can also be caused by poor nutrition or chronic illness.
Alkaline Phosphatase (Alk Phos, ALP)
An elevation in the enzyme ALP often means a problem in the ducts that drain bile from cells inside the liver into and out past the gallbladder to the duodenum (the first part of the small intestine).
Various diseases can cause elevations in ALP, including those that damage or obstruct these ducts. Bone and some other tissues make their own alkaline phosphatases, which could also result in high ALP, even if the liver is working normally.
A normal level of ALP is 44 to 147 units/liter.
Bilirubin
Bilirubin is made as your body breaks down red blood cells. High levels can point to a health condition such as anemia, jaundice, or liver disease.
A total bilirubin (T. Bili) test measures the total amount of bilirubin in the blood. Liver dysfunction results in a buildup of bilirubin in the blood. Since it is yellow, high levels may be suspected even before testing if your skin or the whites of your eyes take on this color. However, total bilirubin levels may be elevated before jaundice becomes visibly apparent.
A normal level is 0.2 to 1.9 mg/100 ml.
Gamma-Glutamyl Transferase (GGT)
GGT is an enzyme found throughout the body, but mostly in the liver. GGT can be elevated in early liver disease, making it a highly sensitive marker. Generally, the test is used to confirm that an elevated ALP is due to this cause. But it is not specific.
Your GGT level 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.
A normal level is 8 to 61 units/liter for males and 5 to 36 units/liter for females.
Follow-Up
If your LFTs are not normal, you may need additional blood tests to determine the reason why. You may also need to have imaging tests so that your healthcare provider can visualize your liver. If results suggest the possibility of a cancer, you may need a biopsy or other testing.
You may also need follow-up LFTs at some point. For example, if you have 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 the tests repeated within a few weeks to monitor your liver function.
With a severe systemic disease, you may need your liver enzymes checked regularly.
Summary
Liver function tests may be part of a routine annual physical, used to shed more light on an acute illness, and to help diagnose liver disease. The tests can also be helpful if you take medications that are known to cause liver problems, underwent an imaging test that showed an abnormality, or have a risk factor associated with liver disease.
From many vantage points, the tests can be very helpful. But while they supply information about liver function, results are not always telling and they cannot confirm a diagnosis.
A Word From Verywell
If you need to have LFTs checked for a chronic condition, it’s a good idea to save your test results in the event you change healthcare providers or hospitals.
A complete record can provide your current care team with critical information that can help them track your disease over time.
Alkaline phosphatase (ALP)Aspartate transaminase (AST)BilirubinGamma-glutamyl transferase (GGT)
ALP - 44-147 units/literAST - 10 to 34 units/literBilirubin - 0. 2 to 1. 9 mg/100 mlGGT (males) - 8 to 61 units/literGGT (females) - 5 to 36 units/liter
Jaundice (yellow skin and eyes)Dark urinePale, bloody, or tarry stoolsEasy bleedingItchinessChillsUpper abdominal painBloody vomitExcessive thirstLight-headedness
