AI Summary Liver fat quantification measures how much fat is in your liver without a biopsy. The CAP score, taken during a FibroScan, is quick and reports fat in dB/m. MRI-PDFF is an MRI scan and the most accurate noninvasive option. Doctors may suggest testing if you have risk factors or abnormal liver blood tests, or to track change over time. A biopsy may still be needed, and weight loss, diet, and exercise often reduce liver fat.
Source: www.liverdirectory.com
Medically Reviewed.
Liver fat quantification means measuring how much fat is in the liver. A healthy liver holds a small amount of fat. Fat becomes a problem when it makes up more than 5% of the liver's weight, a condition called steatosis.
This page explains two tests in this group: the CAP score, which is measured during a FibroScan, and MRI-PDFF, an MRI scan that measures the liver's fat fraction. Neither test needs a biopsy.
Your care team chooses the test that fits your situation. CAP is quick and comes with a liver stiffness reading. MRI-PDFF is the most accurate noninvasive way to measure liver fat.
Below, you will find a side-by-side comparison, who may need each test, what to expect, how to read a CAP score, and answers to common questions.
Liver Health AI Assistant
Ask Aimy
Aimy answers from LiverDirectory’s reviewed health information — helping patients make sense of liver-health terms, prepare for specialist visits, and explore what to look up next.
Liver fat measurement basics
Steatosis is a buildup of fat in liver cells. When it is linked to weight, blood sugar, blood pressure, or cholesterol, doctors call it metabolic dysfunction-associated steatotic liver disease (MASLD). You may also see the older name, nonalcoholic fatty liver disease (NAFLD). Early on, it usually causes no symptoms and is often found during a routine checkup.
Liver fat quantification puts a number on the fat. That number helps your doctor see whether fat is present, how much there is, and whether it changes over time. It works best alongside liver function tests and your medical history.
The two tests on this page measure fat only. A FibroScan also reports liver stiffness in the same visit, but this page focuses on the fat reading.
Fatty liver test options
Each test has its own page with more detail. Here is what sets them apart.
CAP is measured with a FibroScan, a quick ultrasound-based test. A probe on your skin sends sound waves into the liver. Fat weakens, or attenuates, those waves. The more they weaken, the more fat the liver holds. The result is shown in decibels per meter (dB/m).
MRI-PDFF uses an MRI scanner to measure the fraction of the liver made up of fat. It gives a precise, continuous number rather than a broad grade. It is the most accurate noninvasive method for measuring liver fat.
Test comparison guide
Both tests measure liver fat. They differ in how they work and how precise they are.
| Feature | CAP score (FibroScan) | MRI-PDFF |
|---|---|---|
| How it works | A probe on the skin sends painless sound waves into the liver | An MRI scanner uses magnets and radio waves |
| What you lie on | An exam table, on your back, with the right side of your abdomen exposed | A table that slides into a tunnel-shaped scanner |
| What it reports | Fat level in dB/m, plus a liver stiffness reading in the same test | The fat fraction of the liver, as a precise continuous number |
| Accuracy | Good for grading fat; results can be affected by body weight (BMI), probe type, and liver stiffness | The most accurate noninvasive method; closely matches biopsy findings |
| Best suited for | Quick checks and follow-up in a clinic | Precise measurement, and tracking change during treatment |
| Availability | Usually done in a doctor's office or hospital clinic | Where MRI with this software is available |
Your care team decides which test fits your situation, your health history, and what is available near you.
Reasons for testing
A doctor may suggest one of these tests for several reasons.
Obesity, diabetes, and high cholesterol are common risk factors. Fatty liver often causes no symptoms, so testing can find it early.
Abnormal results do not say why the liver is affected. A fat measurement helps your doctor sort out the cause.
Doctors repeat these tests to see whether liver fat changes after lifestyle changes or medical treatment.
Long-term use of medicines that can affect the liver, or a history of heavy alcohol use, may lead your doctor to check for fat.
A test order means your doctor wants more information. Abnormal results are a reason for follow-up, not proof of severe disease.
Preparing for your test
Both tests are painless and need no needles for the measurement itself. Here is how the day usually goes.
Ask your care team if you have questions before the day of your test. Instructions can differ between clinics.
CAP score ranges
Values can vary slightly by machine and by patient.
| Steatosis grade | CAP score (dB/m) | What it suggests |
|---|---|---|
| Normal | Below 238 | Little or no fat |
| S1 (mild) | 238 to 259 | Mild fat buildup |
| S2 (moderate) | 260 to 290 | Moderate fat buildup |
| S3 (severe) | Above 290 | Severe fat buildup |
Reference ranges differ between sources. A cutoff near 275 dB/m is often used to identify fatty liver (5% fat or more) in most situations. Your doctor reads your number in context.
Amsety Bars were designed for people with liver conditions by liver health experts. They offer a convenient way to add energy and nutrients to a liver-friendly diet. Ask your provider what fits your needs.
Explore Liver Health Nutrition Bars
Interpreting your numbers
MRI-PDFF reports the fat fraction as a percentage of the liver. A higher percentage means more fat. Because the number is so precise, doctors can compare scans over time. In studies, a drop of 30% or more in liver fat has been seen with treatment, and doctors read this alongside blood tests and your overall health.
CAP can be affected by body weight, the type of probe, and liver stiffness. A high result does not tell your doctor why fat has built up, and a normal result does not rule out every liver problem. Depending on your results, your doctor may repeat the test, order blood work or more imaging, or suggest a biopsy.
Fat in the liver often improves with weight loss, a balanced diet, and regular exercise. To learn about medical options, see the link below.
Liver Health Coach
Liver health support
BetterLix is a digital liver health support app designed to help you understand liver conditions, track symptoms, and build healthier daily habits. It provides simple, personalized guidance to help you stay informed about your liver health and monitor progress over time.
Common Questions
Yes. A FibroScan with CAP and an MRI-PDFF both measure liver fat without a tissue sample. CAP uses painless sound waves. MRI-PDFF uses an MRI scanner. Each test gives a number that shows how much fat the liver holds. A biopsy is still the only way to tell MASLD from MASH. Your doctor may suggest one if your fat measurement, blood tests, and imaging leave questions.
A CAP score is a number that shows how much fat is in your liver. It comes from a FibroScan. During the test, fat in the liver weakens the sound waves from the probe. The more the waves weaken, the higher the score. The result is shown in decibels per meter (dB/m). A common reference puts a normal result below 238 dB/m. Scores of 238 to 259 suggest mild fat buildup, 260 to 290 moderate, and above 290 severe. Ranges differ slightly between machines, and a cutoff near 275 dB/m is often used to identify fatty liver. Your doctor reads your number in context.
MRI-PDFF is more accurate. It is the most accurate noninvasive method for measuring liver fat, and it closely matches biopsy findings. It gives a precise, continuous number, so doctors can use it to track change over time, including during treatment. CAP is still useful. It is faster, it is done in a clinic, and it comes with a liver stiffness reading. Body weight (BMI), the type of probe, and liver stiffness can affect a CAP result. Your doctor picks the test based on your situation and what is available near you.
No. Both tests are painless, and neither uses radiation. For CAP, you lie on your back with the right side of your abdomen exposed. The operator rests a small probe on your skin over the liver. The test takes about 5 to 15 minutes. For MRI-PDFF, you lie on a table that slides into a tunnel-shaped scanner. You need to stay very still while images are taken. Ask your care team how to prepare, including whether you need to fast.
Not always. A high score means fat is present, but it does not show severe disease by itself. It also does not say why the fat has built up. Your doctor looks at your score with your blood tests, your medical history, and sometimes a liver stiffness reading, which measures scarring. Depending on the results, your doctor may repeat the test or order blood work, more imaging, or a biopsy. An abnormal result is a reason for follow-up, not proof of serious disease.
Medical disclaimer: LiverDirectory provides educational information and a directory of providers. It does not provide medical advice, diagnosis, or treatment. Always consult a licensed physician regarding any medical condition.
