Controlled attenuation parameter (CAP) for the quantification of hepatic steatosis: Relation to body composition in patients with nonalcoholic fatty liver disease

Background: Hepatic fat accumulation is the hallmark of non-alcoholic fatty liver disease (NAFLD) but rapid non-invasive methods measuring hepatic steatosis are not available in clinical practice. The controlled attenuation parameter (CAP™) quantifies the degree of ultrasound attenuation based on vibration controlled transient elastography (VCTE™, FibroScan®; Echosens, Paris). Overweight/obesity is an important risk factor for NAFLD, which is considered to represent the common hepatic phenotype of the metabolic syndrome.

Aim: Our aim was to assess the relationship between body composition and hepatic steatosis, as quantified by CAP in patients referred to the outpatient clinic of a tertiary referral center.

Methods: For this prospective study, we recruited 81 patients with NAFLD (51% men, median age 56 years, range 33 – 78 years). Patients with liver cirrhosis or cancer were excluded. Non-invasive methods were used to quantify both hepatic steatosis (cut-off for significant liver fat accumulation defined as CAP score ≥238 dB/m (Sasso 2010 Ultrasound Med Biol)) and body composition, using an eight electrode body composition analyzer (TANITA BC-418 MA).

Results: The median CAP score was 303 dB/m (range 240 – 400 dB/m). Significant positive associations were observed between CAP score and fat mass (P = 0.001), body mass index (BMI), visceral fat, waist circumference and waist-to-height ratio (all P < 0.0001). An inverse correlation was demonstrated for CAP and fat free mass (P = 0.001). No significant correlation of CAP was found with age, and no differences in median CAP values between women and men were observed. Interestingly however, visceral fat was significantly higher in men (P = 0.001), even though a lower proportion of men as compared to women (46% vs. 65%) were obese (BMI ≥30 kg/m²). Six men and five women presented with marked steatosis and normal fat mass, four of which had a normal BMI (18.5 – 24.9 kg/m²).

Conclusions: CAP represents a rapid non-invasive method that supports the general relationship between increased BMI and body fat and hepatic steatosis. In addition, visceral fat was also positively associated with the degree of hepatic steatosis, as assessed by CAP, a finding which emphasizes the importance of body fat distribution as a risk factor in NAFLD.