Abnormal liver blood tests
Raised liver enzymes can have many causes. A FibroScan with CAP gives a first look at whether fat and scarring are part of the picture, without a biopsy.
AI Summary The CAP score, measured during a painless FibroScan exam, estimates liver fat in decibels per meter (dB/m). Doctors may order it for abnormal liver blood tests, metabolic risk factors, or to monitor liver disease. Scores under 238 dB/m suggest little or no fat, and higher scores mean mild to severe fat. Body size, probe type, and test quality can affect results. A high score leads to follow-up testing, lifestyle changes such as weight loss, and tracking over time.
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CAP Score Measurement
Medically Reviewed.
The CAP score, short for Controlled Attenuation Parameter, estimates how much fat is in your liver. It is measured in decibels per meter (dB/m). A higher number means more fat.
The score comes from a FibroScan exam, a quick and painless test that needs no needles or biopsy. It does not diagnose a condition on its own. Your care team reads it with your blood tests, other imaging, and medical history.
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Controlled Attenuation Parameter
What Is a CAP Score?
Fat buildup in the liver is called steatosis. It is the main feature of fatty liver disease, now called metabolic dysfunction-associated steatotic liver disease (MASLD) and formerly known as NAFLD. The CAP score puts a number on that fat.
During the exam, a probe on your skin sends sound waves into the liver. Fat weakens, or attenuates, those waves. The device measures how much weaker they become and reports the result in dB/m. More fat means a higher score.
The CAP score is measured at the same time as liver stiffness, which reflects scarring (fibrosis). Both numbers come from one FibroScan session, also called transient elastography. Experts recommend measuring CAP alongside transient elastography to assess steatosis.
CAP is an estimate. It has good accuracy for grading steatosis. MRI-PDFF, an MRI-based method, is a more accurate way to measure liver fat where it is available.
CAP Score at a Glance
- Measures liver fat in decibels per meter (dB/m). Higher scores mean more fat.
- Is taken during a FibroScan, together with a liver stiffness reading.
- Is painless and non-invasive. The exam takes roughly 5 to 15 minutes, and results are often ready right away.
- Uses about 275 dB/m as a suggested cutoff for fatty liver (5% or more fat).
- Can be affected by body mass index (BMI), probe type, and liver stiffness.
- Is less precise than MRI-PDFF, the most accurate noninvasive method for measuring liver fat.
Reasons for Liver Fat Testing
Why Your Doctor May Order a CAP Score
A CAP score helps your care team learn whether fat has built up in your liver and how much. Common reasons include:
Metabolic risk factors
Obesity, diabetes, and high cholesterol raise the chance of fatty liver disease. People with these risk factors may be offered the test to check for liver fat.
Monitoring known liver disease
Doctors use FibroScan to follow fatty liver disease, alcohol-related liver disease, hepatitis B and C, and cirrhosis. The CAP score adds the fat measurement to the stiffness reading.
Other reasons for liver stress
Long-term use of medicines that can affect the liver, or a history of heavy alcohol use, may also lead your doctor to order the test.
FibroScan Exam Preparation
How a CAP Score Is Measured
Before the exam
Food can falsely raise the stiffness reading, so experts recommend fasting for at least two hours before the test. Ask your clinic for its exact instructions, and tell the team about your medicines.
During the exam
You lie on your back with the right side of your abdomen exposed. The technician places a small probe on your skin over the liver and takes a series of readings. The exam is painless and usually takes about 5 to 15 minutes.
After the exam
The device reports the CAP score, the stiffness score, and a quality measure. Results are often available right away or soon after. Your doctor explains them in the context of your health history.
CAP Score Range in dB/m
What Your FibroScan Numbers Mean
Your report lists three numbers. The CAP score is the one that estimates liver fat. The other two help your doctor judge scarring and test quality.
CAP score (liver fat)
How much the ultrasound beam weakens as it passes through fat in the liver.
Under 238 dB/m
Lower scores mean less fat in the liver.
Under 238 dB/m: little or no fat.
238 to 259 dB/m: mild steatosis (S1). 260 to 290 dB/m: moderate steatosis (S2). Over 290 dB/m: severe steatosis (S3).
Liver stiffness (scarring)
Measured in kilopascals (kPa). Stiffer tissue suggests more fibrosis. This is a separate result from the CAP score.
Under 5.5 kPa
Lower values mean softer, healthier tissue.
Under 5.5 kPa: no or minimal fibrosis.
5.5 to 7.0 kPa: mild (F1). 7.1 to 9.5 kPa: moderate (F2). 9.6 to 12.5 kPa: severe (F3). Over 12.5 kPa: likely cirrhosis (F4).
Interquartile range (IQR)
A quality check that shows how much the stiffness readings varied during the exam.
Under 30%
Lower variability means more consistent readings.
Under 30% of the median stiffness value: readings are reliable.
Over 30%: the test may need to be repeated.
Cutoffs vary
Guidelines use slightly different cutoffs. About 275 dB/m is suggested to identify fatty liver (5% or more fat), and stiffness cutoffs vary by cause of liver disease. Your doctor interprets your number for your situation.
Accuracy and Test Limitations
What Can Affect Your CAP Score
CAP is a useful screening and tracking tool, but it is an estimate. Several things can affect the number.
Body Size and Probe Type
CAP performance is influenced by BMI, probe type, and liver stiffness. An XL probe is made to reduce failed or unreliable readings in people with obesity.
Measurement Quality
A valid exam needs at least 10 valid measurements, a success rate above 60%, and an IQR under 30%. If these are not met, your doctor may repeat the test.
What It Cannot Show
CAP estimates how much fat is present. It does not show inflammation, and it does not tell your doctor the cause of the fat. Stiffness readings can also be falsely high after eating, with heart failure, bile flow blockage, or heavy alcohol use.
How It Compares With MRI-PDFF
MRI-PDFF is the most accurate noninvasive method for measuring liver fat. It is especially useful for research and tracking treatment, but it is not available everywhere.
Fatty Liver Next Steps
What Happens After a High CAP Score
Follow-Up Testing
A single high score is a reason for follow-up, not a diagnosis. Your doctor may repeat the test, order blood work or more imaging, or in some cases recommend a biopsy for a clearer picture.
Lifestyle Changes
Fatty liver disease can often be reversed. Weight loss of 3% to 5% can improve steatosis, and more than 10% is often needed to improve inflammation and fibrosis. A Mediterranean-style diet and regular physical activity also help.
Tracking Progress
Because CAP is repeatable and non-invasive, doctors can use it over time to see whether liver fat is changing. Ask how often you should be retested and whether to use the same clinic each time.
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Common Questions
Answers to Common CAP Score Measurement Questions
What is a normal CAP score?
A normal CAP score is under 238 dB/m, which means little or no fat in the liver. Higher scores are grouped by how much fat the test detects: 238 to 259 dB/m is mild steatosis (S1), 260 to 290 dB/m is moderate steatosis (S2), and above 290 dB/m is severe steatosis (S3). These ranges are a guide, not a diagnosis. Cutoffs differ slightly between guidelines, and one number does not tell the whole story. Your doctor reads your score alongside your blood tests, other imaging, and medical history.
Does the CAP score show liver scarring?
No. The CAP score estimates how much fat is in the liver. It does not measure scarring. Scarring, called fibrosis, is measured by the liver stiffness result from the same FibroScan exam. That result is reported in kilopascals (kPa), and stiffer tissue suggests more scarring. The two numbers can differ. You can have a high CAP score with little scarring, or the reverse. Your doctor looks at both results together.
Does the CAP test hurt?
No. The exam is painless, and it needs no needles, sedation, or biopsy. You lie on your back with the right side of your abdomen exposed. A technician presses a small probe against your skin over the liver. The probe sends painless sound waves into the liver, and you lie still while it takes a series of readings. The exam usually takes about 5 to 15 minutes. Results are often available right away or soon after.
Do I need to fast before a CAP score test?
Yes, you will likely need to fast. Experts recommend fasting for at least two hours before a FibroScan. Recent food can falsely raise the liver stiffness reading, which is measured in the same exam as your CAP score. Fasting helps keep the results accurate. Clinics may give their own instructions, so follow those first. Tell the team about your medicines when you book or check in.
Is CAP or MRI-PDFF better for measuring liver fat?
MRI-PDFF is more accurate for measuring liver fat. It is the most accurate noninvasive method, and it is especially useful for research and for tracking treatment. It is not available everywhere. CAP is an estimate, but it has good accuracy for grading steatosis. It is quicker, easier to get, and measured in the same session as liver stiffness. Your doctor chooses based on your situation and what is available. If a CAP result is unclear, MRI-PDFF may be a next step.
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.