title: Controlled Attenuation Parameter (CAP): a noninvasive method for the detection of hepatic steatosis based on transient elastography.
abstract: BACKGROUND
  Accurate tools for the noninvasive detection of hepatic steatosis are needed. The Controlled Attenuation Parameter (CAP) specifically targets liver steatosis using a process based on transient elastography.
  
  
  METHODS
  Patients with chronic liver disease and body mass index (BMI) ≥28 kg/m(2) underwent biopsy and liver stiffness measurement (LSM) with simultaneous CAP determination using the FibroScan(®) M probe. The performance of the CAP for diagnosing steatosis compared with biopsy was assessed using areas under receiver operating characteristic curves (AUROC).
  
  
  RESULTS
  A total of 153 patients were included: 69% were male, median BMI was 32 kg/m(2); 47% had nonalcoholic fatty liver disease (NAFLD); and 65% had significant (≥10%) steatosis. The CAP was significantly correlated with the percentage of steatosis (ρ = 0.47) and steatosis grade (ρ = 0.51; both P < 0.00005). The median CAP was higher among patients with significant steatosis (317 [IQR 284-339] vs. 250 [227-279] dB/m with <10% steatosis; P < 0.0005) and the AUROC for this outcome was 0.81 (95% CI 0.74-0.88). At a cut-off of 283 dB/m, the CAP was 76% sensitive, 79% specific, and had positive and negative predictive values of 87% and 64%, respectively. CAP performance was not influenced by measurement variability, but was higher in patients with mild (F0-F1) fibrosis (AUROC 0.89 vs. 0.72 with F2-F4; P = 0.03). The AUROCs of the CAP for ≥5%, >33% and >66% steatosis were 0.79, 0.76 and 0.70, respectively.
  
  
  CONCLUSIONS
  The CAP is a promising tool for the noninvasive detection of hepatic steatosis. Advantages of CAP include its ease of measurement, operator-independence and simultaneous availability with LSM for fibrosis assessment.
authors.affiliation: Liver Unit, Division of Gastroenterology and Hepatology, Department of Medicine, University of Calgary, Calgary, Alberta, Canada. rpmyers@ucalgary.ca
authors.forename: Robert P
authors.initials: RP
authors.lastname: Myers
authors.forename: Aaron
authors.initials: A
authors.lastname: Pollett
authors.forename: Richard
authors.initials: R
authors.lastname: Kirsch
authors.forename: Gilles
authors.initials: G
authors.lastname: Pomier-Layrargues
authors.forename: Melanie
authors.initials: M
authors.lastname: Beaton
authors.forename: Mark
authors.initials: M
authors.lastname: Levstik
authors.forename: Andres
authors.initials: A
authors.lastname: Duarte-Rojo
authors.forename: David
authors.initials: D
authors.lastname: Wong
authors.forename: Pam
authors.initials: P
authors.lastname: Crotty
authors.forename: Magdy
authors.initials: M
authors.lastname: Elkashab
mesh_terms: D000328:Adult; D001706:Biopsy; D015992:Body Mass Index; D016009:Chi-Square Distribution; D002908:Chronic Disease; D054459:Elasticity Imaging Techniques; D005234:Fatty Liver / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging* / Q000473:pathology; D008103:Liver Cirrhosis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D065626:Non-alcoholic Fatty Liver Disease; D009864:Ontario; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index