In short
- Liver stiffness is reported in kilopascals (kPa). Higher usually means more scarring.
- CAP estimates liver fat. It is an estimate, not a percentage.
- The same number means different things in different diseases.
The stiffness score
A healthy liver is soft. Scar tissue makes it stiffer, and the FibroScan measures that stiffness by timing a small vibration as it passes through. The result is in kilopascals. Broadly, low numbers suggest little or no scarring and high numbers suggest advanced scarring, with a grey zone in between.
The catch is that the cut-offs are different for different conditions. A value that is reassuring in fatty liver may be worrying in hepatitis B. Inflammation, a recent meal, heart failure and even a bad probe position can all push the number up. This is why the report comes with a note that it must be interpreted by a clinician.
The CAP score
CAP, in decibels per metre, estimates how much fat is in the liver by measuring how much the ultrasound signal fades. Higher means more fat. It is useful for tracking whether a change in diet is working over time, less useful as a single snapshot.
What to do with the printout
Bring it to the doctor who asked for it, together with your blood tests and any earlier scans. Ask three things: what does this mean for me, is any other test needed, and when should we repeat it. Resist the urge to compare your number with someone else’s, or with a chart on the internet.
Sources
Unfamiliar term? See the liver glossary.