How do I interpret FibroScan liver stiffness (kilopascals) and Controlled Attenuation Parameter (dB/m) values for staging fibrosis and steatosis?

How to Interpret FibroScan Results

FibroScan interpretation requires understanding two key measurements—liver stiffness (LSM in kPa) for fibrosis staging and controlled attenuation parameter (CAP in dB/m) for steatosis grading—with disease-specific cutoffs that vary by etiology and must be validated by technical quality criteria before clinical use. 1

Technical Validity Requirements (Must Check First)

Before interpreting any FibroScan result, verify these three mandatory criteria 1, 2:

• ≥10 successful measurements must be obtained
• Success rate ≥60% is required
• Interquartile range (IQR) <30% of the median value

If any criterion fails, the result is unreliable and should not be used for clinical decisions. 1, 2 Common causes of invalid results include patient movement, inadequate fasting, obesity, narrow intercostal spaces, or operator inexperience. 1, 2

Patient Preparation Requirements

• Fast for at least 4 hours before examination—food intake increases hepatic blood flow and falsely elevates liver stiffness by 15-30%. 1, 2
• Avoid alcohol for at least 1 week in patients with alcohol-related liver disease, as recent consumption artificially raises LSM independent of fibrosis. 1
• Position patient supine with right arm maximally abducted to widen intercostal spaces. 1

Liver Stiffness Measurement (LSM) Interpretation by Disease

NAFLD/MASLD (Most Common Indication)

Use a stepwise approach: calculate FIB-4 first, then proceed to FibroScan only if FIB-4 ≥1.3 (or ≥2.0 if age ≥65 years). 1, 2

LSM cutoffs for NAFLD 1, 2:

• <8.0 kPa: Rules out advanced fibrosis with 93% sensitivity—repeat surveillance in 2-3 years if metabolic risk factors persist
• 8.0-12.0 kPa: Indeterminate zone—refer to hepatology for monitoring and consider repeat testing in 1-2 years
• >12.0 kPa: High probability of advanced fibrosis/cirrhosis—urgent hepatology referral for consideration of liver biopsy or MR elastography

Critical pitfall: Higher CAP values (>300 dB/m) increase false-positive rates for fibrosis detection. 3 In patients with severe steatosis (CAP >338 dB/m), LSM overestimates fibrosis stage by approximately 1-2 stages. 3 When LSM falls in the 8-12 kPa range AND CAP >300 dB/m, consider using FIB-4 or liver biopsy to confirm fibrosis stage. 1

Chronic Hepatitis C

LSM cutoffs for HCV 4:

• <7.0 kPa: Rules out significant fibrosis (≥F2) with 75% sensitivity and 84% specificity
• ≥10.0 kPa: Indicates advanced fibrosis (≥F3) with 87% sensitivity and 88% specificity
• ≥13.0 kPa: Indicates cirrhosis (F4) with 88% sensitivity and 94% specificity

Post-SVR consideration: Do NOT use pre-treatment cutoffs after sustained virologic response—LSM decreases significantly after viral clearance, and patients with pre-treatment cirrhosis require ongoing HCC surveillance regardless of post-SVR LSM values. 1

Chronic Hepatitis B

LSM cutoffs for HBV 4:

• <7.0 kPa: Rules out significant fibrosis (≥F2) with 78% sensitivity and 79% specificity
• ≥8.0 kPa: Indicates advanced fibrosis (≥F3) with 87% sensitivity and 83% specificity
• ≥11.0 kPa: Indicates cirrhosis (F4) with 81% sensitivity and 87% specificity

Critical pitfall: Elevated ALT (>2× ULN) falsely elevates LSM by 20-40% independent of fibrosis. 2 In patients with ALT flares, defer FibroScan until ALT normalizes or use alternative methods like FIB-4. 2

Alcohol-Related Liver Disease

LSM cutoffs for ALD 4:

• <7.8 kPa: Rules out significant fibrosis (≥F2) with 80% sensitivity and 91% specificity
• ≥11.0-12.0 kPa: Indicates advanced fibrosis (≥F3) with 76-87% sensitivity and 81-92% specificity
• ≥15.0-18.0 kPa: Indicates cirrhosis (F4) with 90-93% sensitivity and 85-86% specificity

Note higher cirrhosis thresholds compared to viral hepatitis—this reflects distinct pathophysiology of alcohol-induced injury. 4

Primary Biliary Cholangitis (PBC)

LSM cutoffs for PBC 1, 4:

• <10.0 kPa: Rules out severe fibrosis/cirrhosis—use this as primary screening threshold
• ≥10.7 kPa: Indicates advanced fibrosis (≥F3) with 90% sensitivity and 93% specificity
• ≥16.9 kPa: Indicates cirrhosis (F4) with 93% sensitivity and 99% specificity

Primary Sclerosing Cholangitis (PSC)

Use caution in PSC—patchy fibrosis distribution and biliary strictures can falsely elevate LSM independent of parenchymal fibrosis. 4 Consider MR elastography for more accurate assessment when LSM results are discordant with clinical presentation. 1, 4

LSM cutoffs for PSC 4:

• ≥9.6 kPa: Suggests advanced fibrosis (≥F3) with 90% sensitivity but variable specificity (82-93%)
• ≥14.4 kPa: Suggests cirrhosis (F4) with wide sensitivity range (69-100%) and 88-98% specificity

Controlled Attenuation Parameter (CAP) Interpretation

CAP measures hepatic steatosis severity by quantifying ultrasound attenuation through liver tissue. 1

CAP cutoffs for steatosis grading 1, 5:

• <248 dB/m: No significant steatosis (S0)
• 248-268 dB/m: Mild steatosis (S1, <33% hepatocytes affected)
• 268-280 dB/m: Moderate steatosis (S2, 33-66% hepatocytes affected)
• >280 dB/m: Severe steatosis (S3, >66% hepatocytes affected)

Alternative cutoffs from UK multicenter study 5:

• ≥302 dB/m: Any steatosis (≥S1) with 87% AUROC
• ≥331 dB/m: Moderate-severe steatosis (≥S2) with 77% AUROC
• ≥337 dB/m: Severe steatosis (S3) with 70% AUROC

Normal CAP range in healthy individuals: 156-287 dB/m. 1

Confounding Factors That Affect LSM (Independent of Fibrosis)

Always consider these before interpreting elevated LSM 1, 2:

• Acute hepatitis/ALT flare: Can increase LSM by 2-5 kPa—defer testing until ALT <2× ULN
• Extrahepatic cholestasis: Falsely elevates LSM—check bilirubin and alkaline phosphatase
• Right heart failure/hepatic congestion: Increases LSM by 3-8 kPa—assess jugular venous pressure and perform echocardiography if suspected
• Non-fasting state: Increases LSM by 1-3 kPa—always verify 4-hour fast
• Recent alcohol consumption: Elevates LSM for 1-2 weeks—obtain detailed alcohol history
• Severe obesity (BMI >35): May require XL probe; M probe has 15-20% failure rate in this population 1

Probe Selection

• M probe: Standard probe for patients with skin-to-liver capsule distance <2.5 cm 1
• XL probe: Use when BMI ≥30 kg/m² or skin-to-liver capsule distance ≥2.5 cm 1, 6

Important: XL probe yields lower LSM values (median difference 0.5-1.5 kPa) and higher CAP values (median difference 10-20 dB/m) compared to M probe. 6 Use probe-specific cutoffs when available, or apply caution when comparing serial measurements obtained with different probes. 1, 6

Clinical Scenarios Requiring Urgent Hepatology Referral

Refer immediately when 1, 2:

• LSM >12.5 kPa in any chronic liver disease—indicates high probability of cirrhosis requiring HCC surveillance and variceal screening
• FIB-4 >3.25 or NFS >0.675 regardless of FibroScan result—these scores have 60-80% positive predictive value for advanced fibrosis
• LSM >20-25 kPa—indicates clinically significant portal hypertension (CSPH) with AUROC 0.93, requiring endoscopic variceal screening 2

Follow-Up Testing Intervals

For low-risk patients (LSM <8.0 kPa and FIB-4 <1.3) 1, 2:

• Repeat FIB-4 and FibroScan in 2-3 years if metabolic risk factors persist (diabetes, obesity, metabolic syndrome)
• Repeat in 3-5 years if risk factors are well-controlled

For intermediate-risk patients (LSM 8.0-12.0 kPa) 1, 2:

• Repeat FibroScan annually with hepatology co-management
• Consider liver biopsy if LSM trends upward by >20% or >2 kPa over 1-2 years

For high-risk patients (LSM >12.0 kPa or cirrhosis) 2:

• Monitor with FibroScan every 6 months
• Initiate HCC surveillance with ultrasound ± AFP every 6 months
• Perform esophagogastroduodenoscopy for variceal screening

Common Interpretation Pitfalls to Avoid

1. Using FibroScan without calculating FIB-4 first in NAFLD—this wastes resources and misses the opportunity for simple risk stratification. 1, 2

2. Ignoring CAP values when LSM is 8-12 kPa—severe steatosis (CAP >300 dB/m) increases false-positive rates for fibrosis by 10-15%. 3

3. Applying NAFLD cutoffs to viral hepatitis or vice versa—disease-specific cutoffs differ by 2-5 kPa due to distinct fibrosis patterns. 4

4. Interpreting results without verifying technical validity—IQR >30% renders results unreliable in up to 20% of examinations. 1, 2

5. Using post-SVR LSM values with pre-treatment cutoffs in HCV—LSM decreases 20-40% after viral clearance, but patients with baseline cirrhosis still require surveillance. 1

6. Ordering FibroScan during acute hepatitis or ALT flare—wait until ALT <2× ULN to avoid overestimating fibrosis by 1-2 stages. 2