title: Longer duration of transient elastography predicts unreliable liver stiffness measurements.
abstract: BACKGROUND
  Transient elastography (TE) is a noninvasive, validated method to assess liver fibrosis by obtaining liver stiffness measurements (LSM). However, TE can be limited by unreliable measurement (UM). The relationship between the time taken to perform TE (duration) and UM has not been studied.
  
  
  OBJECTIVE
  To determine whether the duration of TE correlates with UM.
  
  
  METHODS
  We prospectively studied the frequency and predictors of UM over a 5-year period. UM was defined as follows: less than 10 successful measurements, success rate less than 60%, or interquartile range more than 30% of the median LSM value (IQR/LSM>30%).
  
  
  RESULTS
  Among the 2834 patients with LSM analysed, UM occurred in 19.0%. Duration [odds ratio (OR) 4.2, 95% confidence interval (CI) 2.8-6.4; P<0.0001] was the strongest predictor of UM, followed by BMI more than 28 kg/m (OR 2.1, 95% CI 1.5-3.0; P<0.0001), age more than 52 (OR 1.6, 95% CI 1.1-2.3; P=0.007) and non-HBV aetiology (OR 1.6, 95% CI 1.1-2.3; P=0.02). An optimal cut-off of 3 min 47 s was calculated for predicting UM (sensitivity 70%, specificity 65%, OR 4.2, 95% CI 2.7-6.6, P<0.0001). Examinations that took longer than 8 min 10 s had a 90% chance of UM.
  
  
  CONCLUSIONS
  In experienced hands, duration is a strong predictor of UM in patients undergoing TE. Examinations longer than 4 min are more likely to be unreliable. Examinations longer than 8 min are unlikely to yield a valid result and should be considered a futility endpoint. Older age and increased BMI and nonhepatitis B aetiology are independent, albeit weaker, predictors of UM.
authors.affiliation: aDepartment of Gastroenterology, Concord Hospital, Concord bFaculty of Medicine, University of Sydney, Sydney, Australia.
authors.forename: Ken
authors.initials: K
authors.lastname: Liu
authors.forename: Kim Tam
authors.initials: KT
authors.lastname: Bui
authors.forename: Crispin
authors.initials: C
authors.lastname: Corte
authors.forename: Alice
authors.initials: A
authors.lastname: Lee
authors.forename: Meng Chong
authors.initials: MC
authors.lastname: Ngu
authors.forename: Venessa
authors.initials: V
authors.lastname: Pattullo
mesh_terms: D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods* / Q000592:standards; D005260:Female; D006801:Humans; D008099:Liver / Q000503:physiopathology; D008103:Liver Cirrhosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors