CAP Score Interpretation and Liver Fibrosis Assessment
A CAP value of 3 dB/m is extremely low and likely represents a technical error or measurement artifact, as this falls far below any clinically meaningful range for hepatic steatosis assessment. Normal CAP values typically range from approximately 100-400 dB/m, and values below 200 dB/m generally indicate minimal to no steatosis 1.
Understanding CAP Values
The Controlled Attenuation Parameter measures hepatic steatosis (fat content in the liver), not fibrosis. According to EASL guidelines:
- CAP values above 275 dB/m are used to diagnose steatosis with over 90% sensitivity 1
- Typical diagnostic thresholds:
Your reported CAP of 3 dB/m is not physiologically plausible and suggests either:
- Equipment malfunction
- Incorrect probe placement
- Data entry/reporting error
- Misreading of the actual value (possibly 300 dB/m?)
Interpreting Liver Stiffness Measurement (LSM)
For the fibrosis assessment component of your exam, the liver stiffness measurement (expressed in kPa, not dB/m) is what evaluates fibrosis stage:
For NAFLD/Metabolic Liver Disease:
- <8 kPa: Rules out advanced fibrosis 1
- 8.2 kPa: Threshold for significant fibrosis (F≥F2) 2
- 9.7 kPa: Threshold for advanced fibrosis (F≥F3) 2
- 13.6 kPa: Threshold for cirrhosis (F4) 2
Critical Caveat About CAP and LSM Interaction:
Higher CAP values can cause LSM to overestimate fibrosis severity 4, 5. In patients with F0-F2 fibrosis:
- Lower CAP tertile (132-298 dB/m): Mean LSM 6.8 kPa
- Middle CAP tertile (299-338 dB/m): Mean LSM 8.6 kPa
- Higher CAP tertile (339-400 dB/m): Mean LSM 9.4 kPa
This means steatosis itself artificially elevates liver stiffness readings, leading to false-positive results for advanced fibrosis in 7-18% of cases depending on CAP level 4.
Recommended Action
Request a repeat examination immediately to obtain valid CAP and LSM measurements. A CAP of 3 dB/m cannot be used for clinical decision-making. Ensure:
- Proper fasting state (3-4 hours)
- Correct probe selection (M vs XL based on body habitus)
- At least 10 valid measurements with IQR/median <30%
- Review both the CAP (dB/m) and LSM (kPa) values together
Once you have reliable measurements, interpret the LSM for fibrosis staging while accounting for the CAP value—higher steatosis requires higher LSM thresholds to diagnose the same fibrosis stage 4, 5, 6.