Liver Function Test (LFTs) – Normal values, when to order, interpretation

There are a series of blood tests used to diagnose different types of diseases and one of which is LFTs or Liver Function Tests. It is a series of blood tests used to diagnose and monitor the condition of the liver.

It measures the levels of some enzymes and proteins present in the blood. The other terms for liver function tests are liver panel, liver profile hepatic function panel, and liver function panel. The purpose of the test is to check the overall condition of the liver.

The liver is one of the essential body organs. It performs a variety of functions such as getting rid of contaminants from the blood, regulates blood clotting, stores essential vitamins and minerals, get rid of bacteria from the blood, creates factors that fight off infection, produces enzymes, proteins, cholesterols, and bile, helps maintains a balance between different hormones of the body, processes substances that could harm the body, and helps in regulating blood sugar level. ^{(1, 2, 3, and 4)}

Image 1: The image above is a close up look of a human liver.
Picture Source: medicalnewstoday.com

Image 2: The image above shows different representations of the liver with corresponding diseases.
Picture Source: fattyliverguide.com

What is checked during the liver function test/liver panel?

#1 – Liver Proteins

• Total Protein – It measures the total amount of protein present in the blood. The ideal level of total protein is 6.3 to 7.9 g/dL.
• Albumin – It is a type of protein made in the liver. It is responsible for various bodily processes such as nourishing the tissues, stop the leakage of fluid out of the blood vessels, and transports essential substances throughout the body like vitamins, and hormones. Checking the level of albumin is a must as it assesses the capacity of the liver to make a particular protein. A low albumin level is an indicator that the liver is not functioning the way it’s supposed to. It could also be a sign of infection, inflammation, poor nutrition, and kidney-related diseases. The normal albumin level is between 3.5 and 5.0 grams per deciliter.
• Globulin – it is responsible for helping the body fight off infections and regulates the blood’s clotting ability. The normal globulin level ranges between 2.0 and 3.5 g/dL. ^{(2, 3, 4, and 5)}

#2- Liver Enzymes 

Different types of enzymes are made by the liver, which includes ALP or alkaline phosphatase, AST or aspartate aminotransferase, ALT or Alanine transaminase, and GGT or gamma-glutamyl transpeptidase.

•  ALT (Alanine Transaminase) – This enzyme is used by the body to metabolize protein. In the case of liver damage, the level of ALT increases. If the result of the liver panel test showed an abnormal increase in the ALT level, it could indicate liver damage. Although more tests have to be performed to confirm the diagnosis. Further testing is needed if the ALT level is above 25 IU/L for females and 33 IU/L in males as per the American College of Gastroenterology. ^{(4, 6, and 7)}
• AST (Aspartate Aminotransferase) – This enzyme is abundant in the liver, heart, and muscles. It is usually checked in conjunction with the ALT level to check for liver-related problems. A damaged liver triggers the release of AST in the bloodstream. The normal AST level is up to 40 IU/L in adults.
•  ALP (Alkaline Phosphatase) – It is an enzyme abundant in the liver, bones, and bile ducts. The normal level of ALP is up to 120 IU/L in adults. If the level is abnormally high, then it could indicate a blockage in the bile duct, inflammation of the liver, and bone disease. The level of ALP is normally high in children and pregnant women. ^{(4, 5, 6, and 7)}

#3 – Bilirubin

It is a waste product by the liver caused by the breakdown of red blood cells. Bilirubin passes through the liver and excreted through the stool. If there is damage to the liver, it can’t properly process bilirubin leading to an abnormally high level of bilirubin.

The normal bilirubin level ranges between 0.1 and 1.2 milligrams per deciliter.

#4 – Lactate Dehydrogenase

It is an enzyme found in the majority of cells in the body. It is released into the blood when the cells are damaged or injured. The normal level of LD is 122 to 222 U/L.

#5 – Prothrombin Time

It is a type of protein responsible for blood clotting. The normal level of prothrombin time is 9.4 to 12.5 seconds. ^{(2, 5, and 8)}

#6 – Gamma-glutamyltransferase

An enzyme primarily found in the liver but can also be present in other parts of the body such as the kidneys, gallbladder, pancreas, and spleen.

Image 4: A liver function test is one of the parameters used to assess the patient’s overall condition. Here are the various patterns of Liver functions tests according to the cause of liver disease

What is the significance of checking these panels?

If any of the substances mentioned above are outside of the normal range, then it could be an indicator of underlying liver disease such as hepatitis.

The results of the liver function tests are also used as a basis for the progress of treatment of liver disease, check how severely damaged the liver such as in the case of liver cirrhosis, and monitor the side effects of some medications. ^{(1, 3, and 5)}

When a liver function test is ordered?

A liver function test is ordered when you are demonstrating signs and symptoms of liver disease such as:

•     Yellowing of the skin and eyes (jaundice)
•     Diarrhea
•     Nausea and vomiting
•     Abdominal pain
•     Changes in the color of urine (dark-colored urine)
•     Fatigue
•     Changes in the color of the stool (light-colored stool)
•     Weight loss
•     Ascites or collection of fluid in the abdomen
•     Abnormal bleeding/bruising ^{(6, 7, and 8)}

A liver function test is also ordered in people with:

•    A family history of liver disease
•    Severely alcoholic
•    Exposed to hepatitis virus
•    Taking drugs that may cause liver-related damage

Who should submit for a liver function test?

•     People who drink alcoholic beverages a lot.
•     Extremely overweight or obese individuals.
•     Those who have diabetes mellitus.
•     Those who have a high blood pressure level.
•     Those who have a high level of triglycerides.
•     Those who have a condition called hemochromatosis or excessive buildup of iron in the body. ^{(8, 9, and 10)}

How a liver function test is done?

A blood sample is drawn from the vein in your arm using a needle. The extracted blood is placed inside the vial or test-tube. The entire procedure only takes a few minutes (3 to 5 minutes).

Preparation is important to come up with accurate results. Ideally, you are not allowed to eat or drink for at least 10 to 12 hours before the examination.

Refer to the table below for quick information about different liver panel parameters.

Liver Panel Parameter	Normal Range	Increased
ALT (Alanine Transaminase)	7 to 56 units/liter	Viral liver infections Liver cirrhosis Alcohol abuse Shock Hemochromatosis (iron overload) Alcoholic fatty liver Medication overdose such as Tylenol Excessive use of pain medication, a cholesterol-lowering medication, some types of antibiotics, some types of antifungal medications, and seizure and antipsychiatry drugs. (3, 6, and 9)
AST (Aspartate Transaminase)	10 to 40 units per liter	Alcohol abuse Shock Hemochromatosis (iron overload) Alcoholic fatty liver Medication overdose such as Tylenol Excessive use of pain medication, a cholesterol-lowering medication, some types of antibiotics, some types of antifungal medications, and seizure and antipsychiatry drugs. (5, 9, and 10)
Prothrombin Time	9.5 to 13.8 seconds	Vitamin K deficiency Liver disease Coagulation factor deficiencies Side effects of anti-blood-clotting drugs
Albumin	3.5 to 5 g/dL	Dehydration Severe diarrhea
Bilirubin	0.1 to 1.0 mg/dL	Bile duct obstruction Problem in processing bilirubin
ALP (Alkaline Phosphate)	20 to 140 IU/L	Obstructed bile ducts Liver cancer Cirrhosis Bone disease
Lactate Dehydrogenase	100 to 190 U/L	Acute liver disease Liver tumor
Gamma-glutamyltransferase	0 to 30 IU/L	Alcohol-related liver damage Increase the risk of developing some types of cancer

Common patterns of Liver function test (LFT) abnormalities

Are there any limitations?

Although a liver function test measures a lot of biological panels, it has some limitations. The doctor will interpret the result only after considering the patient’s overall health condition – signs and symptoms and past medical and surgical history.

However, you have to keep in mind that the liver function test alone is not the basis of diagnosing a particular condition. What it does is it gives the doctor clues of the likely type of disease a person has. A liver panel test is done in conjunction with other tests and investigations. ^{(4, 6, 9, and 10)}

Bottom line

Problems with the liver are something that should not be taken lightly. They can make you sick. As a matter of fact, some of them are life-threatening.

A liver function test or liver panel test can help assess and diagnose your condition and determine if you need a specific treatment. It is also helpful in assessing the effectiveness of treatment in people receiving treatment for liver-related diseases.

References

1. https://www.healthline.com/health/liver-function-tests
2. https://www.mayoclinic.org/tests-procedures/liver-function-tests/about/pac-20394595
3. https://www.webmd.com/hepatitis/liver-function-test-lft#1
4. https://www.medicinenet.com/liver_blood_tests/article.htm
5. https://www.labtestsonline.org.au/learning/test-index/liver-function
6. https://www.emedicinehealth.com/liver_blood_tests/article_em.htm
7. https://www.medicalnewstoday.com/articles/327369.php
8. https://stanfordhealthcare.org/medical-tests/b/blood-test/types/liver-function-test.html
9. https://thriva.co/hub/liver-function/how-to-test-your-liver-function
10. https://my.clevelandclinic.org/health/diagnostics/17662-liver-function-tests/test-details