What Is FibroScan and How Does It Work?
FibroScan — manufactured by Echosens — is the commercial name for Vibration-Controlled Transient Elastography (VCTE). It is a painless, non-invasive bedside test that takes approximately 10 minutes and does not require sedation, fasting (ideally 2 hours), or any preparation beyond removing clothing from the right side.
The device uses a specialised ultrasound probe placed on the skin over the right lobe of the liver. It generates a low-frequency vibration pulse that propagates as a shear wave through liver tissue. The speed at which this wave travels is directly related to tissue stiffness: a healthy, soft liver transmits the wave more slowly; a stiff, fibrotic liver transmits it faster. The system converts this wave speed into a Liver Stiffness Measurement (LSM) reported in kilopascals (kPa), which maps to fibrosis stages F0–F4.
Simultaneously, the probe measures how ultrasound energy attenuates (diminishes) as it passes through liver tissue — a phenomenon that increases when fat-laden hepatocytes scatter the signal. This attenuation coefficient, called the Controlled Attenuation Parameter (CAP), is reported in decibels per metre (dB/m) and maps to liver fat content (steatosis grades S0–S3). FibroScan thus provides two measurements in one examination: a fibrosis estimate and a steatosis estimate.
Important: FibroScan measures liver stiffness, not fibrosis directly. Stiffness is an excellent proxy for fibrosis under most conditions, but it can be elevated by several non-fibrotic factors — most importantly active liver inflammation (high ALT), recent eating, right heart failure, and cholestasis. Always interpret in clinical context.
Liver Stiffness (kPa): Fibrosis Staging
FibroScan cutoffs vary depending on the underlying liver disease. The values below apply specifically to MASLD (fatty liver disease) patients — the most common clinical context in which FibroScan is used in primary care and hepatology:
| LSM (kPa) | Fibrosis Stage | Clinical Meaning | Typical Next Step |
|---|---|---|---|
| < 7.0–7.9 | F0–F1 | No significant fibrosis | Lifestyle intervention; reassess in 2–3 years |
| 7.9–9.6 | F2 | Significant fibrosis — moderate scarring present | Hepatology referral; consider metabolic optimisation |
| 9.6–13.6 | F3 | Advanced fibrosis — increased cirrhosis risk | Hepatology; 6-monthly surveillance discussion |
| > 13.6 | F4 | Cirrhosis likely | Urgent hepatology; endoscopy; HCC surveillance |
For chronic hepatitis B and C, cutoffs differ (typically higher thresholds for equivalent stages) because inflammation is more pronounced and raises stiffness independent of fibrosis. For alcohol-related liver disease, cutoffs are also shifted higher. Always confirm which disease-specific thresholds your hepatologist is using.
Using FibroScan with FIB-4: The Two-Step Strategy
Current AASLD and EASL guidelines recommend a two-step approach for fibrosis assessment in MASLD. FIB-4 is performed first as a blood-based screen. Patients with indeterminate FIB-4 scores (1.30–2.67) then proceed to FibroScan. This sequential strategy maximises cost-effectiveness while minimising the number of patients who require elastography:
- FIB-4 < 1.30: Low risk — no FibroScan needed in most primary care settings
- FIB-4 1.30–2.67: Indeterminate — FibroScan recommended to resolve uncertainty
- FIB-4 > 2.67: High risk — FibroScan and/or direct hepatology referral
When FibroScan results are available, the AGILE 3+ and AGILE 4 scores combine LSM with FIB-4, age, sex, and diabetes status to provide significantly more accurate fibrosis and cirrhosis probability estimates than either test alone.
CAP Score: Measuring Liver Fat (Steatosis)
The CAP score quantifies hepatic steatosis by measuring how much the ultrasound signal attenuates in fatty tissue. It is expressed in dB/m and measured automatically alongside every FibroScan examination on M or XL probe-equipped devices.
| CAP (dB/m) | Steatosis Grade | Liver Fat Content | Clinical Significance |
|---|---|---|---|
| < 248 | S0 | < 5% of hepatocytes | No steatosis |
| 248–267 | S1 | 5–33% | Mild steatosis — monitor metabolic risk |
| 268–279 | S2 | 34–66% | Moderate steatosis — metabolic intervention indicated |
| ≥ 280 | S3 | > 67% | Severe steatosis — significant MASLD |
CAP is highly sensitive to liver fat and often detects steatosis before it is visible on standard ultrasound. However, it has important limitations: BMI significantly affects CAP readings — higher BMI produces higher CAP values independent of true hepatic fat content. The XL probe tends to yield lower CAP values than the M probe in matched patients. This makes direct comparisons between different probe types unreliable, and BMI-adjusted CAP thresholds are sometimes used in research settings.
M Probe vs XL Probe: Which One Matters for You
FibroScan is available with two probe types, and selecting the correct one is critical to result validity. Using the M probe in a patient who requires the XL probe is one of the most common causes of falsely elevated FibroScan results.
| Feature | M Probe | XL Probe |
|---|---|---|
| Typical indication | BMI < 28–30 kg/m²; standard body habitus | BMI ≥ 28–30 kg/m²; increased waist circumference; thick chest wall |
| Depth of measurement | 25–65 mm below skin surface | 35–75 mm below skin surface |
| When M probe fails | Failed examinations (>10 invalid shots or IQR/M > 30%) should trigger XL probe use | |
| LSM cutoffs | Standard (as above) | Slightly higher — e.g. cirrhosis > 16–17 kPa for some studies |
| CAP values | Higher CAP values | Lower CAP values — not directly interchangeable with M probe |
If your FibroScan report does not specify which probe was used, ask. It matters particularly if you have obesity or if your result is borderline between fibrosis stages.
Quality Criteria: Is Your FibroScan Result Reliable?
Not all FibroScan results are equally reliable. The reported LSM value is the median of 10 individual measurements. Two quality metrics determine whether the result should be trusted:
| Quality Metric | Acceptable | Borderline | Unreliable |
|---|---|---|---|
| IQR/median ratio | < 30% | 30–50% | > 50% |
| Valid shots | ≥ 10 of 10 | 8–9 of 10 | < 8 of 10 |
| Success rate | ≥ 60% | 40–60% | < 40% |
An IQR/median ratio above 30% means the individual measurements were highly variable, which reduces confidence in the median value. This commonly occurs with operator inexperience, patient movement, difficulty locating an adequate measurement window, or the wrong probe type. A result with an IQR/median above 30% should be repeated or supplemented with alternative testing before driving clinical decisions.
Causes of Falsely Elevated FibroScan Results
FibroScan is measuring stiffness, not fibrosis histology. Any condition that independently increases liver stiffness — regardless of the amount of fibrosis present — will inflate the LSM reading. The most clinically important confounders are:
- Active liver inflammation (elevated ALT): Acute hepatitis or ALT > 3–5× ULN can substantially elevate LSM even in the absence of significant fibrosis. Many guidelines recommend checking ALT before FibroScan and postponing if significantly elevated.
- Recent eating: Portal blood flow increases after meals, raising liver stiffness. A 2-hour fast before FibroScan is recommended.
- Right-sided heart failure: Elevated central venous pressure (CVP) is transmitted to hepatic veins, increasing liver stiffness — a phenomenon called congestive hepatopathy. FibroScan should not be used to assess fibrosis in patients with significant right heart failure.
- Extrahepatic cholestasis: Bile duct obstruction causes backpressure that raises liver stiffness independently of fibrosis.
- Acute alcoholic hepatitis: Both inflammation and cholestasis contribute; results are unreliable in this context.
- Amyloidosis: Amyloid deposition stiffens liver tissue regardless of fibrosis stage.