Unified interpretation of liver stiffness measurement by M and XL probes in non-alcoholic fatty liver disease

Objective: The latest model of vibration-controlled transient elastography (VCTE) automatically selects M or XL probe according to patients' body built. We aim to test the application of a unified interpretation of VCTE results with probes appropriate for the body mass index (BMI) and hypothesise that this approach is not affected by hepatic steatosis.

Design: We prospectively recruited 496 patients with non-alcoholic fatty liver disease who underwent VCTE by both M and XL probes within 1 week before liver biopsy.

Results: 391 (78.8%) and 433 (87.3%) patients had reliable liver stiffness measurement (LSM) (10 successful acquisitions and IQR:median ratio ≤0.30) by M and XL probes, respectively (p<0.001). The area under the receiver operating characteristic curves was similar between the two probes (0.75-0.88 for F2-4, 0.83-0.91 for F4). When used in the same patient, LSM by XL probe was lower than that by M probe (mean difference 2.3 kPa). In contrast, patients with BMI ≥30 kg/m² had higher LSM regardless of the probe used. When M and XL probes were used in patients with BMI <30 and ≥30 kg/m², respectively, they yielded nearly identical median LSM at each fibrosis stage and similar diagnostic performance. Severe steatosis did not increase LSM or the rate of false-positive diagnosis by XL probe.

Conclusion: High BMI but not severe steatosis increases LSM. The same LSM cut-offs can be used without further adjustment for steatosis when M and XL probes are used according to the appropriate BMI.