Currently, there is no description of the contribution of the endoscopic ultrasound (EUS)-guided shear wave elastography (SWE) when describing liver fibrosis in patients with screening criteria of metabolic dysfunction-associated steatotic liver disease (MASLD), with absent-to-mild liver fibrosis. Similar research has been published but using vibration-controlled transient elastography (VCTE), recommended mainly due to its lower cost and less invasiveness. However, VCTE is limited to the anatomical proportions of the patient's body, and cannot assess the right hepatic lobe with less reliability, contrary to the EUS-SWE.

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly non-alcoholic fatty liver disease (NAFLD), is an umbrella term which involves simple liver steatosis, metabolic-associated steatohepatitis (MASH) and MASH-related liver cirrhosis. Liver steatosis relies on imaging or biomarkers, but liver biopsy remains the gold standard for its diagnosis and grading. It comprehends intracellular accumulation of triacylglycerol (TAG) as microvascular or macrovascular lipid droplets in at least 5% of hepatocytes. Liver biopsy is invasive, requires a high-quality biopsy sample, can mislead a diagnosis due to sampling bias, depends on pathologist interpretation variability and implies adverse events related to the punction.

There are non-invasive resources useful for the screening and surveillance of liver steatosis and fibrosis. Apart from serum biomarkers, non-invasive technologies designed for this purpose use transabdominal ultrasound (US)-based elastography, namely: US strain, acoustic radiation force impulse (ARFI), point shear wave elastography (pSWE), two-dimension shear wave elastography (2D-SWE) and vibration-controlled transient elastography (VCTE). Although VCTE presents anatomical limitations when used in overweight patients or assessing the right hepatic lobe, it is largely accepted by international guidelines for assessing liver steatosis and fibrosis. Endoscopic ultrasound (EUS)-guided shear wave elastography (SWE) is independent of the anatomical proportions of the patients, and it permits a more reliable right hepatic lobe evaluation. However, it is an invasive and high-cost procedure.

VCTE, US-ARFI and EUS-SWE determine liver fibrosis quantitatively in terms of liver stiffness through kiloPascals. There are four important gaps in the literature: First, the diagnostic accuracy of VCTE for liver steatosis has been profoundly analysed in NAFLD, but in a wide spectrum of liver fibrosis patients, from absent to cirrhosis. These limits finding extrapolations for screening and surveillance. Second, comparisons between VCTE, US-ARFI and EUS-SWE have concentrated on liver fibrosis or cirrhosis, but they have not been compared head-to-head in the context of absent-to-mild liver fibrosis vs controls. Third, there is no determined diagnostic accuracy for EUS-SWE for an early liver fibrosis estimation in MASLD patients. It is useful considering EUS is becoming a more popular procedure. Finally, and to be consequent with the third point, the identification and grading of liver steatosis and fibrosis still need to be described in the nowadays called MASLD patients.

The present study aims to determine the difference in the estimation of liver fibrosis among VCTE, US-ARFI and EUS-SWE in patients with clinical criteria of MASLD screening but absent-to-mild liver fibrosis, according to non-invasive methods.

This study has been called by the authors through the acronym RUMIPAMBA, which means "Role of endoscopic Ultrasound-guided shear wave for MASLD-related liver steatosis and fibrosis Identification in Patients with Absent to Mild Basal fibrosis, based on non-invasive Analytical laboratory tests". In the general culture, Rumipamba is the name of an archaeological prehispanic and preincaic park from Quito, the capital city of Ecuador.

Inclusion Criteria:

• Patients referred for any kind of endoscopic procedure.
• Without clinical suspicion of advanced liver fibrosis.
• Acceptance to participate in the study.

Exclusion Criteria:

• History of greater amounts of alcohol per week (140 g/week and 210 g/week for females and males respectively).
• Significant or advanced fibrosis by Fibrosis-4 Index (FIB4) or the aspartate aminotransferase to platelet ratio index (APRI).
• Any liver space-occupying lesion in the US.
• Comorbidities or conditions related to avoidance of interventional procedures, namely: pregnancy or nursing, coagulopathy or any risk of bleeding, Anaesthesiology Society Association classification IV or higher, New York Heart Association functional class III or IV.

After EUS-SWE, a clinical research coordinator will open the label to confirm the patient's cohort. The patient will undergo the EUS-guided two-lobe liver biopsy only if the patient belongs to the liver steatosis group.