Research ArticleControlled attenuation parameter (CAP) for the diagnosis of steatosis: A prospective study of 5323 examinations
Introduction
Recently, a novel physical parameter based on the properties of ultrasonic signals acquired by the FibroScan® has been developed using the postulate that fat affects ultrasound propagation. This novel parameter, named Controlled Attenuation Parameter (CAP), measures the ultrasound attenuation at the center frequency of the FibroScan® M probe (3.5 MHz) [1]. Values range from 100 to 400 dB/m. CAP can be used for steatosis detection and quantification and present several advantages: it is non-invasive, easy to perform, provides immediate results and is inexpensive in comparison with other measurement modalities. It is less influenced by sampling error than liver biopsy since it explores a liver volume approximately 100 times larger. Furthermore, CAP was designed to target specifically the liver. Therefore, CAP can be performed, simultaneously to liver stiffness measurement and in the same liver volume, making possible the simultaneous evaluation of both fibrosis and steatosis and consequently enhancing the spectrum of non-invasive methods for the exploration and follow-up of patients with chronic liver disease.
Recent studies have shown that CAP is significantly correlated with the percentage of steatosis and steatosis grade, and that median CAP is higher among patients with significant steatosis [2], [3], [4]. In a prospective study of 153 patients, the AUROCs of CAP for ⩾5%, >33%, and >66% steatosis were 0.79, 0.76, and 0.70, respectively [3]. In another prospective study of 112 patients, the AUROCs of CAP for 11 ∼ 33%, 34 ∼ 66%, and >66% steatosis were 0.84, 0.86, and 0.93, respectively [4].
However, transient elastography has limitations: liver stiffness measurement results may be influenced by acute liver injury (as reflected by ALT flares), with a risk of overestimating liver stiffness, and also by extrahepatic cholestasis [5], [6], [7]. The transient elastography interpretation software (for liver stiffness and CAP measurements) indicates whether or not each measurement (or “shot”) is successful. When a shot is considered unsuccessful, the machine provides no result. The entire procedure is considered to have failed when no value is obtained after ten shots or more. Recommandations for successful measurements for CAP measurement are unknown.
The aim of this prospective study was to investigate the frequency and determinants of CAP failure in clinical practice, and to investigate the relationships between CAP and different clinical and biological parameters in a large cohort of consecutive patients.
Section snippets
Study population
Between April 2009 and November 2012, all consecutive patients who presented with chronic liver disease in our centre had CAP performed and were included. These patients were referred to our centre for a non-invasive assessment of liver fibrosis. The following clinical parameters were recorded at the time of measurement: age, gender, body mass index (BMI), waist circumference, hypertension, diabetes, metabolic syndrome, alcohol and coffee use, and indication for measurement. Alcohol abuse was
Characteristics of the study population
A total of 5323 examinations were performed in 4451 patients. Characteristics of patients were as follows: males 54.3%, mean age 54.9 ± 13.4 years, mean BMI 26.6 ± 5.9 kg/m2, 54.1% of patients overweight (BMI [25–30] kg/m2), 22.5% of obese patients (BMI >30 kg/m2), waist circumference 92.7 ± 15.8 cm, diabetes 18.6%, hypertension 36.4%, metabolic syndrome 27.3%, alcohol use 7.7 ± 25.9 drink/week. Causes of chronic liver diseases were as follows: HCV infection 32.8%, Non-alcoholic fatty liver disease (NAFLD)
Discussion
In this prospective study based on more than 5300 examinations – the largest to date – we found that CAP values were significantly associated with all parameters of metabolic syndrome. Our findings may have important implications for current and future applications in patients with metabolic syndrome, especially with NAFLD. Indeed, the increasing prevalence of obesity, insulin resistance and the metabolic syndrome is changing the face of chronic liver disease; in particular, nearly one-third of
Conflict of interest
Victor de Lédinghen received lecture fees from Echosens.
Authors’ contributions
Study concept and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript and critical revision of the manuscript: Victor de Lédinghen; acquisition of data and critical revision of the manuscript: Julien Vergniol, Juliette Foucher, Faiza Chermak, Brigitte Le Bail, Wassil Merrouche, Jean-Baptiste Hiriart, Christophe Cassinotto.
References (27)
- et al.
Controlled attenuation parameter (CAP): a novel VCTE guided ultrasonic attenuation measurement for the evaluation of hepatic steatosis: preliminary study and validation in a cohort of patients with chronic liver disease from various causes
Ultrasound Med Biol
(2010) - et al.
The metabolic syndrome
Lancet
(2005) - et al.
Nonalcoholic steatohepatitis: a proposal for grading and staging the histological lesions
Am J Gastroenterol
(1999) - et al.
Diagnosis and therapy of nonalcoholic steatohepatitis
Gastroenterology
(2008) - et al.
Features, diagnosis, and treatment of nonalcoholic fatty liver disease
Clin Gastroenterol Hepatol
(2012) - et al.
The diagnosis and management of non-alcoholic fatty liver disease: practice guideline by the American Gastroenterological Association, American Association for the Study of Liver Diseases, and American College of Gastroenterology
Gastroenterology
(2012) - et al.
Reproducibility of liver stiffness measurement by ultrasonographic elastometry
Clin Gastroenterol Hepatol
(2008) - et al.
Features associated with success rate and performance of fibroscan measurements for the diagnosis of cirrhosis in HCV patients: a prospective study of 935 patients
J Hepatol
(2007) - et al.
Diagnosis of liver fibrosis and cirrhosis using liver stiffness measurement: comparison between M and XL probe of FibroScan(R)
J Hepatol
(2012) - et al.
The utility of radiological imaging in nonalcoholic fatty liver disease
Gastroenterology
(2002)