SWE Thresholds for Liver Fibrosis in MASLD and Viral Hepatitis: WFUMB 2024
What the WFUMB 2024 Update Changed
WFUMB 2024 updated the 2018 guidelines on liver ultrasound elastography, emphasizing clinical interpretation of liver stiffness considering etiology, measurement quality, and the likelihood of compensated advanced chronic liver disease (cACLD) rather than a 'universal METAVIR by a single number'. For practical work, the most important pSWE/2D-SWE thresholds in kPa and m/s are: around 7 kPa for significant fibrosis, <9 kPa to exclude cACLD, >13 kPa to confirm it, and >17 kPa for suspicion of clinically significant portal hypertension.
Main pSWE/2D-SWE Thresholds
| LSM, kPa | Velocity, m/s | Clinical Interpretation by WFUMB 2024 | Practical Action |
|---|---|---|---|
| ≤5 | ≤1.3 | High likelihood of normal liver stiffness | Assess clinical context and risk factors; dynamic follow-up if low risk |
| ≈7 | ≈1.5 | Threshold for significant fibrosis, indicative of F≥2 | Do not stage in isolation; correlate with biochemistry, platelets, FIB-4, etiology |
| <9 | <1.7 | cACLD unlikely in the absence of other clinical signs | Excludes advanced chronic liver disease in most cases |
| 9–13 | 1.7–2.1 | 'Gray zone': possible cACLD | Repeat quality SWE, use non-invasive tests and clinical context |
| >13 | >2.1 | cACLD probable | Refer for hepatology routing, assessment of complications and portal hypertension |
| >17 | >2.4 | Suspicion of clinically significant portal hypertension | Evaluate spleen, platelets, signs of portal hypertension, and need for endoscopy |
MASLD/MAFLD: How to Apply Thresholds
In MASLD, liver stiffness depends not only on fibrosis. Results are influenced by steatohepatitis activity, steatosis severity, body mass index, technical window, inflammation, cholestasis, and congestive hemodynamics. Therefore, WFUMB 2024 recommends using SWE as part of a multiparametric ultrasound and clinical-laboratory algorithm.
In practical protocols for MASLD, it is advisable not to label 'F2' or 'F3' as a final diagnosis based on a single measurement. More accurately: 'liver stiffness corresponds to the range of significant fibrosis', 'cACLD unlikely', 'value in the gray zone 9–13 kPa', or 'cACLD probable'. Such language reduces the risk of overdiagnosing cirrhosis during inflammatory or metabolic exacerbation.
Viral Hepatitis B and C
In chronic viral hepatitis, the relationship between LSM and fibrosis is better validated than in MASLD, but staging should not be mechanical. Necro-inflammatory activity, elevated transaminases, cholestasis, and postprandial state can overestimate stiffness. After successful antiviral therapy, a decrease in LSM may reflect reduced inflammation, not just regression of collagen fibrosis.
For HBV/HCV, a threshold around 7 kPa serves as a guide for significant fibrosis, <9 kPa helps exclude cACLD, and >13 kPa supports the diagnosis of advanced chronic liver disease. For values >17 kPa, actively seek signs of portal hypertension, especially with thrombocytopenia and splenomegaly.
pSWE and 2D-SWE: What to Include in the Report
The report should specify the method: pSWE or 2D-SWE, equipment and probe, measurement units, median LSM, number of valid measurements, and quality criteria if available on the system. Do not mindlessly transfer thresholds between VCTE, pSWE, and 2D-SWE: WFUMB considers them as different technologies with similar but not identical evidence bases.
If the device outputs velocity in m/s, do not manually 'improve' the protocol by converting to kPa without understanding the manufacturer's algorithm. In a clinical article, it is permissible to refer to kPa/m/s pairs provided in the consensus, but in the protocol, it is better to retain the original units of the device.
Measurement Quality Requirements
SWE is performed fasting, intercostally, in the right lobe, away from large vessels, the capsule, and focal lesions. Measurements are taken during calm breath-holding, without deep inspiration and without probe compression. In obesity, narrow intercostal spaces, severe steatosis, and ascites, the likelihood of technical error is higher.
Repeat examination is indicated if the value does not align with the clinical picture: for example, LSM >13 kPa with normal platelets, no splenomegaly, and low FIB-4; or conversely, LSM <9 kPa with clear ultrasound signs of portal hypertension. In such cases, the WFUMB approach requires not 'choosing a favorite number' but re-verifying quality and comprehensive assessment.
How to Formulate Fibrosis Stage
The optimal formulation is probabilistic. Example: '2D-SWE of the liver: median 8.2 kPa. Value above the threshold for significant fibrosis but below the threshold for exclusion/confirmation of cACLD; correlation with FIB-4, platelets, and etiology recommended.' For 11 kPa: 'range 9–13 kPa, gray zone cACLD.' For 15 kPa: 'value above threshold >13 kPa, cACLD probable.'
This format is more useful than categorical 'F3' or 'F4', especially in MASLD. For viral hepatitis, comparison with METAVIR is permissible, but clinical decisions should still consider disease activity and therapeutic status.
Typical Interpretation Pitfalls
- Acute inflammation: elevated ALT/AST can overestimate LSM.
- Cholestasis: mechanical or intrahepatic bile retention increases stiffness regardless of fibrosis.
- Congestive liver: right heart failure and venous congestion cause false elevation.
- Food before examination: postprandial blood flow increases stiffness, so fasting is required.
- Focal changes: measurements near a tumor, cyst, vessel, or capsule are invalid for diffuse fibrosis.
Clinical Conclusion
For the ultrasound diagnostic physician, the WFUMB 2024 update provides a clear scale: around 7 kPa for significant fibrosis, <9 kPa makes cACLD unlikely, 9–13 kPa is an indeterminate range, >13 kPa makes cACLD probable, >17 kPa indicates a risk of clinically significant portal hypertension. In MASLD and viral hepatitis, these values should be used as standardized clinical stratification, not as an automatic morphological stage without context consideration.
Frequently asked questions
Can 2D-SWE immediately indicate F2, F3, or F4?
It is better to provide a probabilistic interpretation: significant fibrosis, gray zone cACLD, cACLD probable. WFUMB 2024 emphasizes the dependence of thresholds on etiology, method, measurement quality, and clinical context.
What is the main threshold for excluding advanced liver disease?
For pSWE/2D-SWE, a value <9 kPa, or <1.7 m/s, in the absence of other signs makes cACLD unlikely.
What does liver stiffness >17 kPa mean?
This is the range of suspicion for clinically significant portal hypertension. It is necessary to evaluate platelets, spleen, collaterals, ascites, and route the patient through a hepatological algorithm.