Transient elastography: should XL probe be used in all overweight patients?

Background: Obesity is one of the main factors of transient elastography (TE) failure, considering body mass index (BMI) ≥28 kg/m² as a limiting factor. The XL probe was designed to overcome this limitation. Aim: To compare the feasibility of the M and XL probes in patients with BMI ≥ 28 kg/m², to evaluate differences in mean values of controlled attenuation parameter (CAP) and liver stiffness measurement (LSM) between the two probes and find predictive factors of TE failure. Material and methods: Prospective study, including all patients with BMI ≥ 28 kg/m² consecutively admitted for TE. Results: Included 161 patients. Measurements with M probe were reliable in 69.6% of the patients, with 68.2% of valid measurements in obese population and 58.9% in patients with skin-capsule distance (SCD) >25 mm. In 40 patients (81.6%) with an invalid M probe measurement, a reliable result was obtained with XL probe. We found that SCD >25 mm was the only predictor of M probe failure (OR: 4.9, CI: 1.64-14.63, p = .004). In those patients in which TE was possible with both probes (n = 112), mean CAP was 304 ± 49 dB/m² with M probe and 301 ± 50 dB/m² with XL probe (p = .59). Regarding liver stiffness, a mean value of 7.58 ± 3.47 kpas was obtained with the M probe and 6.21 ± 3.44 kpas with the XL probe (p < .001). Conclusion: There is a reliable applicability of the M probe in a high number (68.2%) of patients with a BMI ≥30 kg/m². A SCD >25 mm was the only predictive factor of M probe failure. Mean values of LSM with XL probe were lower than those obtained with M probe.