Diagnosis of NAFLD & NASH

How do doctors diagnose NAFLD and NASH?

Doctors use your medical history, a physical exam, and tests to diagnose nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

Medical history

Your doctor will ask if you have a history of health conditions that make you more likely to develop NAFLD and NASH, such as

Your doctor will ask about diet and lifestyle factors that may make you more likely to develop NAFLD and NASH, such as a lack of physical activity or a habit of drinking beverages with added sugar.

Medical tests can’t show whether alcohol is the cause of fat in your liver. Your doctor will ask about your alcohol intake to find out whether fat in your liver is a sign of alcoholic liver disease or NAFLD.

Doctor talking with a patient and taking notes.
Your doctor will ask if you have a history of health conditions that make you more likely to develop NAFLD and NASH.

Physical exam

During a physical exam, a doctor usually examines your body and checks your weight and height to calculate your body mass index. Your doctor will look for signs of NAFLD or NASH, such as

  • an enlarged liver
  • signs of insulin resistance such as darkened skin patches over your knuckles, elbows, and knees
  • signs of cirrhosis, such as jaundice, a condition that causes your skin and whites of your eyes to turn yellow

What tests do doctors use to diagnose NAFLD and NASH?

Doctors use blood tests, imaging tests, and sometimes liver biopsy to diagnose NAFLD and NASH.

Blood tests

A health care professional may take a blood sample from you and send the sample to a lab. Your doctor may suspect you have NAFLD or NASH if your blood test shows increased levels of the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Your doctor may perform additional blood tests to find out if you have other health conditions that may increase your liver enzyme levels.

Imaging tests

Your doctor may use the following imaging tests to help diagnose NAFLD:

  • Ultrasound. Ultrasound uses a device called a transducer, which bounces safe, painless sound waves off your organs to create an image of their structure.
  • Computerized tomography (CT) scans. CT scans use a combination of x-rays and computer technology to create images of your liver. For a CT scan, a health care professional may give you a solution to drink and an injection of a special dye, called contrast medium. Contrast medium makes the structures inside your body easier to see during the procedure. You’ll lie on a table that slides into a tunnel-shaped device that takes the x-rays.
  • Magnetic resonance imaging (MRI). MRI machines use radio waves and magnets to produce detailed images of your organs and soft tissues without using x-rays. A health care professional may give you an injection of contrast medium. With most MRI machines, you’ll lie on a table that slides into a tunnel-shaped device. Some machines allow you to lie in a more open space; examining the liver can be more difficult with these machines.

A technician performs these tests in an outpatient center or a hospital. A technician can perform an ultrasound in a doctor’s office as well. A radiologist reads and reports on the images. You don’t need anesthesia, although you may receive light sedation during an MRI if you have a fear of confined spaces.

Imaging tests can show fat in your liver. These tests can’t show inflammation or fibrosis, so your doctor can’t use these tests to find out whether you have simple fatty liver or NASH. If you have cirrhosis, imaging tests may show nodules, or lumps, on your liver.

Liver biopsy

During a liver biopsy, a doctor will take a piece of tissue from your liver. A pathologist will examine the tissue under a microscope to look for signs of damage or disease.

A doctor performs a liver biopsy at a hospital or an outpatient center. A health care professional will tell you how to prepare for a liver biopsy. You may need to stop taking certain medicines to prepare. You may be asked not to eat or drink anything for 8 hours before the procedure. During the procedure, you may receive a local anesthetic, sedatives, and pain medicine.

During the biopsy, you’ll lie on a table with your right hand resting above your head. The doctor will numb the area where he or she will insert the biopsy needle with a local anesthetic and then use the needle to take a small piece of liver tissue.

A liver biopsy is the only way to detect liver inflammation and damage to diagnose NASH. Doctors don’t recommend this test for everyone with NAFLD. Your doctor may recommend a liver biopsy if you are more likely to have NASH or if your other tests show signs of advanced liver disease or cirrhosis.

Drawing of a liver biopsy procedure. A liver is drawn within an outline of a male body. A needle pricks a piece of the liver tissue. An arrow points away from the spot where the needle touches the liver toward a slide with the tissue sample. The liver is labeled.
During a liver biopsy, a doctor will take a piece of tissue from your liver. A pathologist will examine the tissue with a microscope to look for signs of damage or disease.
November 2016
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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.

The NIDDK would like to thank:
Anna Mae Diehl, M.D., Duke University Medical Center, and Brent A. Tetri, M.D., Saint Louis University