How and when to propose the Hepatic Steatosis Index (HSI)?

Hepatic Steatosis Index (HSI): Development and Clinical Application

The Hepatic Steatosis Index (HSI) was developed by Lee et al. in 2010 based on a Korean cohort of 5,462 patients and should be proposed for non-invasive screening of hepatic steatosis in patients with metabolic risk factors, particularly when imaging tools are unavailable or impractical. 1

What is the HSI?

The HSI is a simple non-invasive serum panel that uses readily available clinical parameters to assess the presence of hepatic steatosis. The formula is:

HSI = 8 × (ALT/AST ratio) + BMI (kg/m²) + 2 (if diabetes) + 2 (if female)

When to Use HSI

HSI should be used in the following clinical scenarios:

• As a screening tool in large epidemiological studies where imaging is impractical 1
• In patients with metabolic risk factors (obesity, diabetes, dyslipidemia) 1
• When ultrasound or other imaging modalities are unavailable 1
• For initial risk stratification before deciding on more expensive or invasive testing 1

Interpretation of HSI Values

• HSI < 30: Rules out hepatic steatosis with 93.1% sensitivity 1
• HSI > 36: Indicates hepatic steatosis with 92.4% specificity 1
• HSI between 30-36: Indeterminate range requiring additional testing 1

Advantages of HSI

• Simple calculation using routine clinical parameters
• Validated in both Asian and Western populations 1
• Good diagnostic performance with AUC of 0.81 1
• Can effectively exclude steatosis with high negative predictive value 1, 2
• Correlates with metabolic syndrome and inflammatory markers 2

Limitations and Caveats

• Not recommended as first-line tool when imaging is available 1
• Performance may be slightly reduced in patients receiving antiviral therapy for chronic hepatitis B (AUC 0.707 vs. 0.779 in untreated patients) 3
• Should not be used alone for diagnosis but rather as a screening tool 1
• Less accurate than MRI-PDFF for quantifying steatosis 1

Clinical Algorithm for Steatosis Assessment

1. Initial screening: Calculate HSI in patients with metabolic risk factors

   • If HSI < 30: Low probability of steatosis, routine follow-up
   • If HSI > 36: High probability of steatosis, proceed to imaging confirmation
   • If HSI 30-36: Indeterminate, proceed to imaging

2. Confirmation: Ultrasound as first-line imaging tool 1

   • Widely available and inexpensive
   • Good for moderate-severe steatosis detection

3. Advanced assessment (if needed):

   • Controlled Attenuation Parameter (CAP) with values >275 dB/m suggesting steatosis 1
   • MRI-PDFF for precise quantification in research settings 1

4. Monitoring: Repeat HSI calculation every 1-3 years based on risk profile 4

Comparison with Other Non-invasive Indices

HSI performs comparably to other indices but has advantages in simplicity:

• Fatty Liver Index (FLI): More complex calculation requiring triglycerides, BMI, GGT, and waist circumference; AUC 0.85 1
• NAFLD Liver Fat Score (NLFS): Requires fasting insulin measurement; AUC 0.86-0.87 1
• Hepatorenal Index: Ultrasound-based method requiring specialized measurement; more operator-dependent 5, 6

HSI has been shown to be particularly effective in patients with type 1 diabetes with an AUC of 0.75, though slightly less accurate than FLI (AUC 0.86) in this population 2.

In conclusion, HSI represents a practical, accessible tool for initial screening of hepatic steatosis, particularly valuable in resource-limited settings or large population studies where imaging-based assessment may not be feasible.