A FibroScan is a non-invasive ultrasound technology used to assess liver health. The test uses transient elastography to measure liver stiffness and a Controlled Attenuation Parameter (CAP) to measure fat content, helping doctors determine the degree of liver damage. The resulting report provides a snapshot of your liver’s condition, offering metrics on the two primary forms of liver disease: fibrosis (scarring) and steatosis (fatty change).
Identifying the Core Data Points
A standard FibroScan report centers on two distinct, independently measured values. The first is the Liver Stiffness Measurement (LSM), which quantifies the degree of scarring (fibrosis) present in the tissue. This value is reported in kilopascals (kPa), reflecting how stiff the liver is.
The second core measurement is the Controlled Attenuation Parameter (CAP) score, which measures the amount of fat accumulation (steatosis) in the liver. The CAP score is expressed in decibels per meter (dB/m). These two metrics track different pathological processes, allowing for simultaneous assessment of both fat content and scarring.
Decoding Liver Stiffness Scores
The kPa reading is used to assign a grade on the METAVIR F-staging system, which ranges from F0 (no fibrosis) to F4 (cirrhosis). A healthy liver typically shows an LSM reading between 2 and 7 kPa. Minimal fibrosis (F0 or F1) generally corresponds to values below 7 kPa.
Moderate fibrosis (F2) typically falls between 7 and 11 kPa, while severe fibrosis (F3) is often represented by scores between 11 kPa and 14 kPa. Cirrhosis (F4) often exceeds 14 kPa, though values above 12.5 kPa are frequently used as a general cutoff. The exact cut-off values for each F-stage can vary based on the specific type of chronic liver disease, such as chronic hepatitis C versus non-alcoholic steatohepatitis (NASH).
Other factors can temporarily influence the LSM reading, potentially leading to an overestimation of fibrosis. Conditions like acute inflammation, liver congestion, or a lack of fasting prior to the scan can artificially elevate the stiffness score. Therefore, the LSM result is always evaluated alongside a patient’s complete medical history and other laboratory tests.
Understanding the Fatty Liver Assessment
The CAP score measures how much the ultrasound signal is weakened as it passes through the liver; higher attenuation indicates a greater presence of fat. The CAP score is used to determine the steatosis grade, which follows the S-staging system (S0 to S3). This system correlates the CAP score to the percentage of liver cells containing fat.
A normal liver (S0) typically has a CAP score below 238 dB/m, meaning less than 11% of the liver is affected. Mild steatosis (S1) ranges from 238 to 260 dB/m, reflecting 11% to 33% fat infiltration.
Moderate steatosis (S2) falls between 260 and 290 dB/m, correlating to 34% to 66% of the liver being affected. Severe steatosis (S3) is indicated by scores above 290 dB/m, meaning more than 67% of the liver tissue contains fat. A higher CAP score signifies a greater degree of fat accumulation, often associated with conditions like Non-Alcoholic Fatty Liver Disease (NAFLD).
Evaluating the Quality of the Scan
The reliability of your FibroScan results is assessed through technical data points included on the report. One measure is the Success Rate, which reflects the number of valid measurements obtained. A reliable scan requires a high success rate, at least 60%, to ensure the data accurately represents the liver tissue.
The Interquartile Range (IQR) is another measure of reliability, showing the variability among the individual liver stiffness readings. A low IQR suggests consistent measurements, leading to a more trustworthy median LSM value. If the ratio of the IQR to the median LSM is less than 30%, the result is considered reliable.
Factors such as severe obesity or the presence of fluid in the abdomen (ascites) can make obtaining a reliable reading difficult. A technically poor scan may not accurately reflect the true state of liver health, regardless of the resulting kPa and CAP numbers.