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Understanding Liver Function Tests

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Understanding Liver Function Tests

Everyone has a liver but not everyone understands exactly what it does or why it’s so important. Surprisingly, the liver has numerous roles (upwards of 500!) in the body to help ensure good health. A few key roles include processing nutrients from food, making bile, removing toxins from the blood, and metabolizing medications.

When the liver is damaged and not working as it should, say, in the case of hepatitis or fatty liver disease, serious problems can occur. Because the liver is an organ that you can’t do without, you need to do what it takes to protect it. One way for your health care provider to assess the health of your liver is to order a series of tests called liver function tests.

What are liver function tests?

Liver function tests, or LFTs, for short, are blood tests that measure different enzymes, proteins, and other substances, such as bilirubin, that are made by the liver.

Some of these tests reveal how well the liver is doing its usual functions. Other LFTs measure enzymes released by the liver in response to damage or disease.

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Why are liver function tests ordered?

Your health care provider may order LFTs for a number of reasons, which include:

  • Diagnosing a liver disease, such as hepatitis, especially if you have symptoms
  • Monitoring the status of a liver disease to see how well treatment is working
  • Assessing the extent of liver damage or scarring by a disease, such as cirrhosis
  • Monitoring side effects of certain medicines, which may include statins, antibiotics, NSAIDs (nonsteroidal anti-inflammatory medicines), antiseizure medicines, and tuberculosis medicines
  • Checking your liver health if you have certain medical conditions, such as diabetes, high blood pressure, gallbladder disease, anemia, or hemochromatosis
  • Checking for damage from frequent alcohol use

What are some symptoms that could indicate a need to have liver function tests?

Your provider might recommend that you have LFTs if you have the following symptoms:

  • Jaundice, a condition that causes your skin and eyes to turn yellow
  • Nausea and vomiting
  • Diarrhea
  • Abdominal pain
  • Dark-colored urine
  • Light-colored stool
  • Fatigue

What are the different types of liver function tests?

There are a number of LFTs, and your provider may order all of them or just a few of them. Some LFTs are included in a routine comprehensive metabolic panel (CMP), along with other tests, including glucose, albumin, electrolytes, and tests for kidney function.

LFTs are blood tests, so they require a blood sample from a vein in your arm. Some of the common LFTs are:

Alanine transaminase (ALT)

ALT is an enzyme that helps convert protein into energy. It’s released by the liver into the blood if it’s damaged or not working properly. A normal result is 7-55 units per liter (U/L). (Note that normal results listed can vary from lab to lab, and may be different for women and children).

Aspartate aminotransferase (AST)

This is an enzyme that’s found in various organs of the body, including the liver, pancreas, brain, heart, and muscles. AST helps metabolize amino acids. Increased levels of this enzyme in blood can indicate certain diseases or muscle damage. A normal result is 8-48 U/L.

Alkaline phosphatase (ALP)

This enzyme is found in the liver and the bones, and helps break down protein. ALP can check how the liver’s bile ducts are working. A normal result is 40-129 U/L.

Albumin and total protein

Albumin is one of the proteins made by the liver; levels of albumin may be low if there is long-standing liver disease. Total protein levels can be normal in the presence of liver disease, but levels can increase with hepatitis. A normal albumin result is 3.5-5 grams per deciliter (g/dL). A normal total protein result is 6.3-7.9 g/dL.

Bilirubin

Bilirubin is made from the breakdown of red blood cells. It passes through the liver and is excreted in the stool. High levels can indicate liver damage or anemia. A normal bilirubin result is 0.1-1.2 mg/dL.

Gamma-glutamyl transferase (GGT)

This is another enzyme made by the liver. High levels in the blood could indicate liver or bile duct damage. A normal GGT result is 8-61 U/L.

L-lactate dehydrogenase (LD)

LD (also known as lactic acid) is an enzyme found in the liver, as well as many other tissues, including the heart, brain, lungs and skeletal muscle. It helps make energy. When any of these tissues are damaged, LD is released into the blood and may signify damage from disease or injury. A normal LD result is 122-222 U/L.

Prothrombin time (PT)

Prothrombin is a protein that helps blood to clot. PT is the time it takes for blood to clot. A high PT may indicate liver damage, but it might also be high due to taking blood-thinning medicines, too. A normal PT result is 9.4-12.5 seconds.

Your provider will determine which tests to order, based on factors such as symptoms, existing liver disease, certain medical conditions that you have, or medications that you’re taking. They should also discuss your test results with you and, if the result is outside of the normal range, explain what this means. Abnormal results may not always be a sign of liver damage or disease: burns, infections, muscle damage, and pregnancy may cause some LFTs to be abnormal. Be sure to ask your provider if you have questions about your results.

What happens next if liver function test results are not normal?

Based on the results of your LFTs, your provider may do further testing, including more blood tests, for hepatitis or other diseases that can affect the liver. You might need a liver biopsy to check for fatty liver disease, cirrhosis, or cancer, for example. You might also need imaging tests, such as an ultrasound, a CT scan, or an MRI.

Want to learn more about protecting your liver? Read “Diabetes and NAFLD” and “Preventing Fatty Liver (NAFLD).”

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES on social media

A Registered Dietitian and Certified Diabetes Educator at Good Measures, LLC, where she is a CDE manager for a virtual diabetes program. Campbell is the author of Staying Healthy with Diabetes: Nutrition & Meal Planning, a co-author of 16 Myths of a Diabetic Diet, and has written for  publications including Diabetes Self-Management, Diabetes Spectrum, Clinical Diabetes, the Diabetes Research & Wellness Foundation’s newsletter, DiabeticConnect.com, and CDiabetes.com

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