A FibroScan is a non-invasive medical test that uses ultrasound technology to assess liver health. It measures the stiffness and fat content within the organ, providing insights into its condition.
Key Components of a FibroScan Report
A FibroScan report highlights two main measurements: liver stiffness (LSM or E), quantified in kilopascals (kPa), and the Controlled Attenuation Parameter (CAP), which measures liver fat in decibels per meter (dB/m). The report may also include quality metrics, such as the Interquartile Range to Median ratio (IQR/M), which helps assess the reliability of the liver stiffness reading.
Interpreting the Liver Stiffness Score
The liver stiffness score directly relates to the degree of fibrosis, or scarring, in the liver. A lower kPa value suggests less scarring, indicating a healthier liver. Conversely, higher kPa values point towards increased scarring. Normal liver stiffness results typically fall between 2 and 7 kPa.
Healthcare providers use these kPa values to assign a fibrosis score, commonly ranging from F0 to F4. A score of F0 or F1 indicates no scarring or only mild scarring. A score of F2 suggests moderate scarring, while F3 signifies severe scarring. An F4 score represents advanced scarring, often referred to as cirrhosis.
For individuals with Non-Alcoholic Fatty Liver Disease (NAFLD), specific kPa ranges are often used for interpretation: 2 to 7 kPa for F0-F1, 7.5 to 10 kPa for F2, 10 to 14 kPa for F3, and 14 kPa or higher for F4. It is important to remember that these ranges can vary based on the underlying cause of liver disease.
Understanding the CAP Score
The Controlled Attenuation Parameter (CAP) score provides a quantitative measure of steatosis, which refers to the accumulation of fat within the liver. This score is expressed in decibels per meter (dB/m) and ranges from approximately 100 dB/m to 400 dB/m. A lower CAP score signifies less fat in the liver, indicating a healthier state.
Healthcare providers utilize the CAP score to determine the steatosis grade, typically categorized from S0 to S3. A CAP score below 238 dB/m generally suggests a normal amount of fatty change, often corresponding to an S0 grade (less than 5% liver fat). A CAP score between 238 and 260 dB/m indicates S1, or mild fatty liver, affecting 11% to 33% of the liver.
Scores ranging from 260 to 290 dB/m are classified as S2, representing moderate fatty liver, where 34% to 66% of the liver is affected by fat. A CAP score of 290 dB/m or higher corresponds to S3, indicating severe fatty liver with 67% or more of the liver impacted by fatty changes. Understanding the CAP score helps distinguish the severity of fatty liver disease independently from liver scarring.
Factors Influencing Report Accuracy
Several factors can influence the accuracy of FibroScan results, particularly the liver stiffness score. Consuming food or drink shortly before the test can artificially elevate the stiffness measurements, making it advisable to fast for a few hours prior to the procedure. Acute liver inflammation, which can stem from recent liver illness or alcohol consumption, may also lead to an overestimation of liver scarring.
Liver congestion, often a consequence of conditions like heart failure, can similarly result in higher-than-actual stiffness readings due to increased fluid within the liver. Technical difficulties during the procedure, such as those encountered with individuals having a high body mass index (BMI greater than 30) or fluid accumulation in the abdomen (ascites), can also affect the reliability of the measurements.
Ultimately, a healthcare provider integrates the FibroScan results with other diagnostic tools, including blood tests, imaging scans, and the patient’s overall clinical history, to form a comprehensive diagnosis.