FibroScan Results Explained: What Your CAP and kPa Mean

TL;DR

• A FibroScan report has two main numbers: liver stiffness in kPa, a stand-in for scarring, and CAP in dB/m, a rough measure of liver fat.
• In fatty liver, stiffness under 8 kPa makes advanced scarring unlikely, 8–12 kPa is a gray zone, over 12 kPa makes advanced fibrosis likely, and 20 kPa or more is associated with cirrhosis (AASLD).
• CAP cutoffs vary between guidelines (roughly 248–288 dB/m for fatty liver), and food, inflammation or heavy drinking can push stiffness up. One scan is read alongside your blood tests, not on its own.

A FibroScan gives you two numbers: liver stiffness in kilopascals (kPa), which estimates scarring, and a CAP score in decibels per meter (dB/m), which estimates fat. In fatty liver, a stiffness under 8 kPa makes advanced scarring unlikely, while readings over 12 kPa suggest it’s likely and usually lead to a specialist review.

If you’ve just had the scan, the report can look like a wall of numbers. This guide walks through each one: what your kPa and CAP mean, how to tell whether the exam was reliable, what can throw it off, and what usually happens next.

What Is a FibroScan?

FibroScan is the best-known machine for vibration-controlled transient elastography (VCTE). You lie on your back with your right arm raised, and the operator holds a probe against the skin between your ribs on the right side, over the liver. The probe sends painless, low-frequency vibrations into the liver, and the machine measures how fast they travel through it. The scan itself takes only a few minutes.

The same scan produces two measurements:

• Liver stiffness (LSM), in kPa. Scar tissue makes the liver stiffer, so this is the number used to estimate fibrosis.
• Controlled attenuation parameter (CAP), in dB/m. This measures how much the ultrasound signal fades (attenuates) in the liver. Higher values go with more fat.

There are two main probe sizes. The standard M probe suits most people, and the XL probe is used for people with obesity. European guidelines note that using both probes as needed brings the failure rate below 5%.

Doctors usually order a FibroScan when a first blood-based score, FIB-4, isn’t clearly low. You can check yours with our FIB-4 calculator.

What Does My kPa Number Mean?

These are the AASLD cutoffs for MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD), and the European guideline uses the same 8 and 12 kPa thresholds.

Liver stiffness	What it means in fatty liver	Usual next step
Under 8 kPa	Advanced fibrosis can be ruled out	Lifestyle changes; your doctor rechecks FIB-4 periodically
8–12 kPa	Gray zone: may go with some scarring (fibrotic MASH), but advanced fibrosis is neither confirmed nor ruled out	Referral to a liver specialist for further evaluation is usually advised
Over 12 kPa	Advanced fibrosis is likely	Specialist care; sometimes more tests to confirm
20 kPa or more	Associated with cirrhosis	Cirrhosis care, including liver cancer and varices screening

Two caveats matter. First, a high reading isn’t a certainty: the AASLD notes that above 12 kPa the positive predictive value is low, between 0.34 and 0.71 in studies, so some people above that line don’t have advanced scarring on a biopsy. Second, these cutoffs are for fatty liver measured with FibroScan. Other liver diseases use different thresholds, and other machines (shear wave elastography, MR elastography) use different cutoffs, even though they also report kPa.

Your report and your doctor’s reading win over any general table. No single scan is a diagnosis: your doctor will look at the trend and your other results, including your platelet count and FIB-4. Over time, the AASLD notes that a rise in stiffness of 20% may be linked to disease progression.

What Does My CAP Score Mean?

CAP is a rough grade of liver fat, not a precise measurement. The grades below come from a large pooled analysis that both the 2021 and 2024 European guidelines cite. Treat them as approximate.

CAP score	Approximate fat grade
Below 248 dB/m	No significant fat (S0)
248 dB/m and above	At least mild fat (S1)
268 dB/m and above	At least moderate fat (S2)
280 dB/m and above	Severe fat (S3)

Cutoffs vary. The 2021 European guidance says there are no agreed cutoffs and that values above 275 dB/m might be used to diagnose fatty liver. The AASLD lists 288 dB/m. CAP is also influenced by factors such as diabetes and body weight, and the AASLD states that it does not accurately quantify or monitor changes in liver fat. MRI-PDFF (an MRI fat scan) does that better, but it costs more and isn’t a quick in-clinic test.

So a CAP of 300 dB/m tells you there’s likely a fair amount of fat. It doesn’t tell you about scarring, and a lower CAP on your next scan isn’t proof of progress on its own. Scarring, not fat, is what best predicts future liver problems, which is why the stiffness number matters more.

How Do I Know My FibroScan Was Reliable?

Your stiffness result is the median of a series of readings. Three quality markers often appear next to it:

• Number of valid readings: traditionally at least 10.
• Success rate: traditionally at least 60% of attempts.
• IQR/median: how spread out the readings were. Traditionally 30% or less.

A 2013 study of 1,165 patients found that the IQR/median ratio mattered most. Exams with a ratio of 10% or less were “very reliable.” Exams with a ratio above 30% and a median of 7.1 kPa or higher were “poorly reliable,” correctly classifying cirrhosis about 70% of the time versus 86–90% for the others. If your report shows a high IQR/median, ask whether the scan should be repeated.

Getting a good reading can be harder with obesity or fluid in the abdomen (ascites), and it depends on the operator’s experience. The XL probe helps in larger bodies.

What Can Make a FibroScan Read Falsely High?

Stiffness reflects more than scar tissue. The 2021 European guidelines list several things that can make it overestimate fibrosis:

• Eating recently. A meal raises stiffness, so the guideline requires at least 3 hours of fasting.
• Liver inflammation, such as a hepatitis flare or very high liver enzymes.
• Blocked bile flow (obstructive cholestasis).
• Liver congestion, for example from heart failure.
• Exercise shortly before the scan.
• Heavy drinking. When stiffness is high and AST or GGT is more than twice the upper limit, the guideline advises repeating the scan after at least a week without alcohol or with reduced drinking. Our GGT guide explains that test.

If your stiffness is high but your other results don’t fit, these are the first things to rule out.

What Are FAST and Agile Scores?

Some FibroScan reports add combined scores that mix the scan with blood tests:

• FAST combines stiffness, CAP and AST to flag “at-risk” MASH, meaning inflammation plus at least moderate scarring. The AASLD lists below 0.35 as the rule-out cutoff and 0.67 or above as the rule-in cutoff.
• Agile 3+ and Agile 4 combine stiffness with the AST/ALT ratio, platelet count, sex and diabetes status (plus age for Agile 3+). They were developed to identify advanced fibrosis (Agile 3+) and cirrhosis (Agile 4) more accurately than stiffness alone in people seen in liver clinics.

These scores help specialists decide who needs closer follow-up or a biopsy. Your doctor will explain your number if it appears on the report.

What Happens After a FibroScan?

That depends on the stiffness, your blood tests and your other health conditions:

• Low stiffness (under 8 kPa): usually back to your regular doctor, with periodic FIB-4 checks and a focus on weight, diet, activity and alcohol.
• Intermediate or high stiffness: the AASLD advises referral to a gastroenterologist or hepatologist for further evaluation. That might include MR elastography or, less often, a biopsy.
• 20 kPa or more, or other signs of cirrhosis: cirrhosis care, with liver cancer screening every 6 months and checks for varices. Nutrition priorities also change, as our cirrhosis diet guide explains.

Whatever the result, the main levers are the same. For people carrying extra weight, the 2024 European guideline aims for a sustained weight loss of at least 5% to reduce liver fat, 7–10% to improve inflammation and 10% or more to improve fibrosis. Our guide on how to reverse fatty liver covers the plan, and ALT and AST levels in fatty liver explains how the scan fits with your blood tests.

How to Prepare for a FibroScan

1. Fast for at least 3 hours beforehand, or as your clinic instructs.
2. Skip hard exercise right before the appointment.
3. Avoid heavy drinking in the days before, and be honest about your usual intake.
4. Mention heart failure or a recent illness, since congestion and inflammation can raise the reading.
5. Ask for your full report, including the IQR/median, so you can compare future scans. Our guide to liver function test results helps you read the blood tests that go with it.

The Bottom Line

A FibroScan gives you two numbers. Stiffness in kPa is the important one for scarring: in fatty liver, under 8 kPa is reassuring, 8–12 kPa is a gray zone, over 12 kPa makes advanced fibrosis likely, and 20 kPa or more points toward cirrhosis. CAP is a rough grade of liver fat, with cutoffs that vary between guidelines. Check that the exam was reliable, remember that food, inflammation and alcohol can push stiffness up, and let your doctor read the scan together with your FIB-4 and blood tests.

Sources

• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)
• EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis, 2021 update (Journal of Hepatology)
• EASL–EASD–EASO Clinical Practice Guidelines on the management of MASLD (Obesity Facts 2024)
• Boursier et al. Determination of reliability criteria for liver stiffness evaluation by transient elastography (Hepatology 2013)
• Sanyal et al. Enhanced diagnosis of advanced fibrosis and cirrhosis in individuals with NAFLD using FibroScan-based Agile scores (Journal of Hepatology 2023)

This article is for informational purposes only and is not medical advice. Talk to your doctor or hepatologist about your specific situation.