Accuracy of Controlled Attenuation Parameter for Assessing Liver Steatosis in Individuals With Morbid Obesity Before Bariatric Surgery

Federica Tavaglione; Antonio De Vincentis; Vincenzo Bruni; Ida Francesca Gallo; Simone Carotti; Dario Tuccinardi; Giuseppe Spagnolo; Ester Ciociola; Rosellina Margherita Mancina; Oveis Jamialahmadi; Rossella D'Alessio; Bruna Bottazzi; Silvia Manfrini; Antonio Picardi; Giuseppe Perrone; Paolo Pozzilli; Marco Caricato; Umberto Vespasiani-Gentilucci; Stefano Romeo


Liver International. 2022;42(2):374-383. 

In This Article

Abstract and Introduction


Background & Aims: The ultrasound-based controlled attenuation parameter (CAP) is a non-invasive tool widely validated for assessing liver steatosis across different etiologies. However, few studies, with liver biopsy available, have investigated its performance in individuals with morbid obesity. Herein, we aimed to evaluate the diagnostic accuracy of CAP in participants with morbid obesity from the MAFALDA study before bariatric surgery.

Methods: A total of 120 individuals with valid examinations within three months from bariatric surgery were included. Clinical, laboratory, FibroScan® (XL probe), and liver biopsy data were collected using standardized procedures. The overall accuracy of CAP for detecting liver steatosis was estimated by the area under the receiver-operating characteristics curve (AUROC). Optimal cut-offs were chosen at points with the highest Youden index.

Results: The AUROCs of CAP for detecting S ≥ S1, S ≥ S2, and S = S3 were 0.91 (95% CI 0.86–0.97), 0.83 (95% CI 0.76–0.90), and 0.86 (95% CI 0.79–0.94), respectively. The best CAP cut-offs for S ≥ S1, S ≥ S2, and S = S3 were 300 dB/m (95% CI 275–316), 328 dB/m (95% CI 296–345), and 344 dB/m (95% CI 343–352), respectively. CAP values were independently influenced by steatosis grade (estimate 20.60, 95% CI 12.70–28.40, P = 1.05 × 10−6). The AUROC of FibroScan-AST (FAST) score for detecting progressive non-alcoholic steatohepatitis was 0.76 (95% CI 0.66–0.86).

Conclusions: In individuals with morbid obesity, CAP measured by XL probe is an accurate non-invasive tool for grading liver steatosis. Measurement of liver fat content by CAP may help identify those eligible for bariatric procedures and estimate the effect of bariatric surgery on hepatic steatosis.

Lay Summary: The ultrasound-based controlled attenuation parameter (CAP) by using the XL probe has an excellent performance for grading liver steatosis among individuals with morbid obesity.

CAP may represent an accurate tool for the non-invasive assessment of liver steatosis among individuals with morbid obesity before and after bariatric surgery.


Non-alcoholic fatty liver disease (NAFLD) is becoming the major cause of chronic liver disease worldwide, paralleling the epidemics of obesity and type 2 diabetes. The prevalence of NAFLD in the general population is estimated to be approximately 25% but it reaches over 90% among individuals with severe obesity undergoing weight loss procedures.[1]

NAFLD/non-alcoholic steatohepatitis (NASH) are serious obesity-related complications and their presence qualifies individuals to be eligible for bariatric surgery.[2] Therefore, an accurate diagnosis and staging of NAFLD play an important role in the clinical management of obesity and decision-making on the most appropriate treatment modality (ie, lifestyle changes, pharmacological therapy, or bariatric surgery).

Although the stage of liver fibrosis is the main determinant of liver-related outcomes,[3] the degree of liver fat accumulation has a crucial role in the physiopathology of NAFLD and is causally related to liver damage.[4,5] Consistently, novel drugs under clinical investigation for the treatment of NAFLD primarily target the reduction of liver steatosis.[6]

To date, liver biopsy represents the most accurate technique for the assessment of hepatic steatosis, necroinflammation, and fibrosis.[7] However, this procedure is considered invasive and accompanied by a low, but not negligible, risk of complications, including hepatic bleeding, perforation of adjacent organs, and infection.[8] Therefore, in the last years, an intensive effort has been carried out to identify reliable non-invasive diagnostic tests for NAFLD/NASH detection and to follow its course over time.

The ultrasound-based controlled attenuation parameter (CAP) is a non-invasive tool for the assessment of liver steatosis. CAP has primarily been validated among individuals with chronic liver disease due to different etiologies, including NAFLD and viral hepatitis.[9–12]

To reduce the failure rate of transient elastography with the M probe due to high body mass index (BMI), the XL probe has been recently developed and specifically designed for individuals with overweight/obesity (skin-to-liver capsular distance ≥25 mm).[13–15] Several studies have examined the feasibility of XL-CAP for liver steatosis among individuals with overweight/obesity.[12,15–20] However, a handful of histologically characterized cohort studies have specifically investigated the use of CAP for assessing liver steatosis in individuals with morbid obesity.[21–23]

The aim of this study was to evaluate the diagnostic accuracy of CAP measured by the XL probe to detect liver steatosis in participants with morbid obesity from MAFALDA, a study in which liver biopsy was available. Additionally, we assessed the performance of FibroScan-AST (FAST) score[24] for detecting progressive NASH (NASH + NAFLD activity score NAS ≥ 4 + F ≥ F2) in this cohort.