The FibroScan procedure, scientifically known as Vibration-Controlled Transient Elastography (VCTE), offers a non-invasive method for assessing liver health. This specialized ultrasound technology sends a mechanical wave into the liver and measures its speed through the tissue. This measurement translates into two parameters: the Liver Stiffness Measurement (LSM), which indicates scarring or fibrosis, and the Controlled Attenuation Parameter (CAP), which quantifies fat buildup or steatosis. VCTE has significantly reduced the reliance on invasive liver biopsy, allowing for easier monitoring of chronic liver diseases like non-alcoholic fatty liver disease (NAFLD) and viral hepatitis.
Defining the Normal Range for Liver Stiffness (kPa)
The Liver Stiffness Measurement (LSM) reflects the amount of fibrosis (scarring) present in the liver. This result is quantified in kilopascals (kPa), where a higher kPa value indicates a stiffer, more scarred liver. For a generally healthy individual without known liver disease, the normal range for liver stiffness is typically reported between 2 and 7 kPa, with many healthy people measuring below 5.3 kPa.
A result within this lower range corresponds to minimal or no fibrosis, classified as stages F0 to F1 on the standardized Metavir scoring system. F0 represents no fibrosis, while F1 indicates only mild scarring or portal fibrosis, meaning the liver architecture remains largely intact. This minimal stiffness level is generally considered a normal outcome for liver health assessment.
Interpretation of the kPa value shifts based on the patient’s underlying health condition, necessitating a specialist’s review. For example, a result of 7 kPa is considered the upper limit of normal for most causes of chronic liver disease, including NAFLD and chronic hepatitis B or C. However, the thresholds for identifying more advanced disease are disease-specific.
As the kPa value increases, it correlates with more severe stages of liver damage. A reading suggesting moderate scarring (F2) generally falls into the 7 to 11 kPa range, depending on the specific disease. Values exceeding 14 kPa indicate advanced liver scarring, known as cirrhosis (F4).
The stiffness measurement is a semi-quantitative value and not an absolute diagnosis. A result of 2 to 7 kPa indicates a high probability of a healthy liver or only mild damage, but it does not completely exclude the possibility of significant underlying disease. The LSM is an indicator that specialists use alongside blood tests and clinical history to determine the true state of liver health.
Interpreting the CAP Score for Liver Fat (dB/m)
The second measurement provided by the FibroScan is the Controlled Attenuation Parameter (CAP), which quantifies hepatic steatosis (excess fat in liver cells). This measurement utilizes the same ultrasound technology but focuses on the attenuation, or weakening, of the sound wave as it travels through the fatty tissue. The CAP score is expressed in decibels per meter (dB/m) and ranges from 100 dB/m to 400 dB/m.
A normal liver is expected to have a low CAP score, typically below 238 dB/m, corresponding to minimal or no fat buildup (less than 5% of liver cells affected). As fat increases, the CAP score rises and is categorized into the steatosis staging system (S0 to S3), where S0 signifies a healthy liver.
The CAP score of S1 represents mild steatosis, affecting 11% to 33% of the liver tissue, which generally falls between 238 dB/m and 260 dB/m. Moderate steatosis, or S2, means that 34% to 66% of the liver is affected by fat, corresponding to a CAP score between 260 dB/m and 290 dB/m. A result of S3, indicating severe steatosis, is given for scores higher than 290 dB/m, where more than two-thirds of the liver cells contain fat deposits.
The CAP score is independent of the liver stiffness (kPa) score, meaning a patient can have a normal stiffness score but a high CAP score, or vice versa. This distinction is important because steatosis and fibrosis can progress at different rates or exist in isolation. Monitoring the CAP score allows physicians to track the effectiveness of interventions aimed at reducing liver fat, such as diet and lifestyle changes.
Situational Factors Affecting FibroScan Accuracy
Certain physiological conditions can temporarily influence the liver’s stiffness, leading to a potentially inaccurate or artificially elevated kPa result. Acute liver inflammation, such as a flare-up of hepatitis or other liver illness, can cause the organ to swell and stiffen, resulting in a higher kPa value that does not reflect true long-term fibrosis. Similarly, severe liver congestion, often caused by right-sided heart failure, can temporarily increase the stiffness measurement due to increased blood volume within the organ.
External conditions or patient preparation can also skew the results. Eating a large meal shortly before the examination can temporarily affect the measurement, leading to a higher stiffness reading. The presence of ascites (fluid accumulation in the abdomen) can interfere with wave transmission, causing the test to be unreliable or fail. Furthermore, a high Body Mass Index (BMI) or significant subcutaneous fat can limit the accuracy of the probe. These factors necessitate careful patient preparation, including fasting, and require the physician to correlate VCTE results with the full clinical picture.