FibroScan: Where Does It Stand in US Practice
FibroScan: Where Does It Stand in US Practice
There are some consistent themes regarding VCTE test performance across etiologies of liver disease. Because of the mechanism of data acquisition, any process that interferes with the depth of the liver examined in relation to the probe may affect measurement success. For example, ascites precludes the applicability of VCTE but is less critical to clinicians assessing patients for advanced liver disease. Important LSM confounders include obesity, inflammation, cholestasis, congestion, and food intake (Figure 1).
The reproducibility of VCTE has been examined by multiple groups first in 2007 by Fraquelli et al. This group studied 800 VCTE examinations, 2.4% of which yielded indeterminate results. Factors significantly associated with reduced interobserver agreement included increased body mass index (BMI) (25 kg/m or greater), steatosis, and low fibrosis stages. Similarly, in a study of healthy subjects, the rate of VCTE failure (0 valid acquisitions) increased with BMI, reaching an 88% failure rate for BMI greater than 40 kg/m. Confirming these trends, Castera et al showed how in their prospective database of 13,369 VCTE examinations, rates of failure and unreliable examinations (less than 10 valid acquisitions or success rate <60% or interquartile range less than 30% of median value) occurred in 3.1% and 15.8% of exams, respectively. Failure was most associated with BMI greater than 30 kg/m (odds ratio [OR], 7.5) and operator experience of fewer than 500 exams (OR, 2.5). The same applied for unreliable exams: BMI greater than 30 kg/m (OR, 3.3) and operator inexperience (OR, 3.1).
Beyond obesity, essentially any process that alters hepatic viscoelastic properties can affect LSM. Hepatic inflammation, acute or chronic, can lead to falsely elevated LSM. Whereas bland steatosis itself does not affect VCTE, steatohepatitis does. Extrahepatic cholestasis, passive cardiogenic congestion or central venous hypertension, amyloid deposition, and meal ingestion (at least in cirrhotic patients) have each been shown to influence liver stiffness as measured by VCTE.
Finally, operator experience may play a role. In general, operators need to have done more than 100 examinations, perhaps more than 500, before operator experience is no longer a confounding variable.
In summary, there are several factors that must be addressed to ensure the quality of information obtained from VCTE. We currently recommend at least 10 measurements of liver stiffness with an interquartile range of <0.3 and a success rate greater than 60%. Some authorities recommend that at least 70% of measurements be valid, but this has never really been studied and compared with liver biopsy. Patients should fast at least 3 hours. Consideration and correction should be made for alanine aminotransferase (ALT) levels above 100 IU/L. Finally, we recommend a history and physical exam to assess for evidence of known confounding variables.
Keep These Limits in Mind
There are some consistent themes regarding VCTE test performance across etiologies of liver disease. Because of the mechanism of data acquisition, any process that interferes with the depth of the liver examined in relation to the probe may affect measurement success. For example, ascites precludes the applicability of VCTE but is less critical to clinicians assessing patients for advanced liver disease. Important LSM confounders include obesity, inflammation, cholestasis, congestion, and food intake (Figure 1).
The reproducibility of VCTE has been examined by multiple groups first in 2007 by Fraquelli et al. This group studied 800 VCTE examinations, 2.4% of which yielded indeterminate results. Factors significantly associated with reduced interobserver agreement included increased body mass index (BMI) (25 kg/m or greater), steatosis, and low fibrosis stages. Similarly, in a study of healthy subjects, the rate of VCTE failure (0 valid acquisitions) increased with BMI, reaching an 88% failure rate for BMI greater than 40 kg/m. Confirming these trends, Castera et al showed how in their prospective database of 13,369 VCTE examinations, rates of failure and unreliable examinations (less than 10 valid acquisitions or success rate <60% or interquartile range less than 30% of median value) occurred in 3.1% and 15.8% of exams, respectively. Failure was most associated with BMI greater than 30 kg/m (odds ratio [OR], 7.5) and operator experience of fewer than 500 exams (OR, 2.5). The same applied for unreliable exams: BMI greater than 30 kg/m (OR, 3.3) and operator inexperience (OR, 3.1).
Beyond obesity, essentially any process that alters hepatic viscoelastic properties can affect LSM. Hepatic inflammation, acute or chronic, can lead to falsely elevated LSM. Whereas bland steatosis itself does not affect VCTE, steatohepatitis does. Extrahepatic cholestasis, passive cardiogenic congestion or central venous hypertension, amyloid deposition, and meal ingestion (at least in cirrhotic patients) have each been shown to influence liver stiffness as measured by VCTE.
Finally, operator experience may play a role. In general, operators need to have done more than 100 examinations, perhaps more than 500, before operator experience is no longer a confounding variable.
In summary, there are several factors that must be addressed to ensure the quality of information obtained from VCTE. We currently recommend at least 10 measurements of liver stiffness with an interquartile range of <0.3 and a success rate greater than 60%. Some authorities recommend that at least 70% of measurements be valid, but this has never really been studied and compared with liver biopsy. Patients should fast at least 3 hours. Consideration and correction should be made for alanine aminotransferase (ALT) levels above 100 IU/L. Finally, we recommend a history and physical exam to assess for evidence of known confounding variables.
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