What is the interpretation and management of a high Controlled Attenuation Parameter (CAP) score indicative of liver steatosis?

Interpretation and Management of High CAP Score

A CAP value above 275 dB/m indicates the presence of hepatic steatosis with over 90% sensitivity, and management should focus on addressing the underlying metabolic risk factors through lifestyle modification, metabolic syndrome treatment, and assessment for advanced fibrosis rather than repeat steatosis quantification. 1

CAP Score Interpretation

Diagnostic Thresholds

For detecting any steatosis (>5%):

• CAP ≥263-275 dB/m has high sensitivity (>90%) and positive predictive value (>90%) for detecting steatosis 1
• The EASL guidelines specifically recommend values above 275 dB/m as the threshold for diagnosing steatosis 1
• Korean guidelines suggest slightly lower cutoffs: 271 dB/m for mild steatosis in Asian populations 1

For quantifying steatosis severity:

• 248-268 dB/m: Mild steatosis (5-33%) 1
• >250-285 dB/m: Moderate steatosis (34-66%) 1
• >280-310 dB/m: Severe steatosis (>66%) 1

Important Caveats

CAP values are influenced by several factors that must be considered:

• BMI: CAP increases by approximately 4.4 dB/m per BMI unit 2
• Diabetes: Shifts CAP values upward by approximately 10 dB/m 2
• NAFLD/NASH etiology: Increases CAP by approximately 10 dB/m compared to viral hepatitis 2
• Ethnicity: Western populations show higher cutoffs (302-337 dB/m) compared to East Asian populations (250-290 dB/m) 1

Quality criteria matter:

• CAP measurements with IQR >40 dB/m have decreased accuracy and should be interpreted cautiously 1
• The XL probe has much lower failure rates (3-4%) compared to the M probe (21%) and should be used preferentially in obese patients 1

Clinical Management Algorithm

Step 1: Confirm Steatosis and Assess Severity

If CAP >275 dB/m:

• Steatosis is present with high confidence 1
• Do not repeat CAP for quantification - CAP has suboptimal performance (AUROC 0.70-0.77) for distinguishing between steatosis grades 1
• Consider MRI-PDFF only if precise quantification is needed for clinical trials or specific therapeutic decisions, as it outperforms CAP 1

Step 2: Evaluate for Advanced Fibrosis (Critical Priority)

This is the most important step because fibrosis stage, not steatosis grade, determines prognosis and mortality risk. 1

Perform liver stiffness measurement (LSM) by transient elastography:

• LSM <8 kPa: Rules out advanced fibrosis 1
• LSM ≥8 kPa: Requires further evaluation with patented tests (ELF, FibroMeter, FibroTest) or consideration of liver biopsy 1

Calculate FIB-4 score:

• FIB-4 <1.3: Rules out advanced fibrosis 1
• FIB-4 >1.3: Requires LSM by transient elastography and/or patented serum tests to rule-out/in advanced fibrosis 1

Step 3: Address Underlying Etiology and Metabolic Risk Factors

Identify and treat the cause of steatosis:

• Screen for metabolic syndrome components (diabetes, hypertension, dyslipidemia, obesity) 2
• Assess for alcohol use (detailed quantification of grams/day)
• Evaluate for viral hepatitis (HBV, HCV) 2
• Review medications that can cause steatosis (corticosteroids, amiodarone, methotrexate, tamoxifen)

Implement lifestyle modifications:

• Target 7-10% weight loss through caloric restriction and increased physical activity
• This is the only proven intervention to reduce steatosis and improve liver histology in NAFLD
• Address insulin resistance with metformin if diabetic or pre-diabetic

Step 4: Surveillance Strategy

For patients with steatosis but no advanced fibrosis (LSM <8 kPa, FIB-4 <1.3):

• Repeat LSM yearly to monitor for fibrosis progression 1
• Do not repeat CAP routinely - focus on clinical parameters (weight, metabolic control) rather than repeat steatosis quantification 1

For patients with advanced fibrosis or cirrhosis:

• Follow standard hepatocellular carcinoma surveillance protocols
• LSM values remain predictive of outcomes even after treatment of underlying disease 1

Common Pitfalls to Avoid

Do not use CAP as a first-line screening tool - ultrasound remains the most widely used and cost-effective first-line method for detecting steatosis, despite its limitations 1

Do not rely on CAP alone in obese patients (BMI >30) - accuracy decreases significantly, with AUROC dropping to 0.58-0.64 for moderate-severe steatosis 3

Do not use non-invasive scores (FLI, NLFS, HSI) for clinical diagnosis of steatosis - these are not recommended in clinical practice per EASL guidelines 1

Do not focus excessively on steatosis quantification - the presence of NASH and degree of fibrosis are far more important for prognosis than the exact percentage of steatotic hepatocytes 1

Remember that liver biopsy remains the reference standard for diagnosing NASH - none of the available non-invasive tests, including CAP, can reliably diagnose NASH 1