Which Ultrasound to Order for NAFLD Assessment
Standard abdominal ultrasound is the recommended first-line imaging modality for NAFLD screening and initial assessment, but you should not rely on it for grading steatosis severity or making treatment decisions based on its severity classification. 1, 2
Primary Recommendation: Standard Abdominal Ultrasound
Order a standard B-mode abdominal ultrasound as your initial imaging study for suspected NAFLD in adults and children, as recommended by multiple international guidelines including EASL and KASL 3, 1, 2
Ultrasound is practical for serial assessments due to universal availability, real-time capability, relatively low cost, and no radiation exposure 1
It can evaluate the entire hepatobiliary system beyond just steatosis, helping identify structural liver or gallbladder problems 3, 1
Critical Limitations You Must Understand
Do not use ultrasound grading (mild/moderate/severe) for clinical decision-making because of unacceptably high misclassification rates 3, 1:
Children classified as "mild" steatosis by ultrasound had moderate steatosis on liver biopsy in approximately 50% of cases 3, 1
Patients graded as "moderate" steatosis by ultrasound showed the full spectrum from mild to severe on biopsy, with MRI fat fractions ranging from normal to near maximal 3
Ultrasound has a positive predictive value of only 47-62% for fatty liver in children 3
Sensitivity drops significantly when steatosis is less than 30% 1, 4
Performance is particularly poor in obese patients 1
Ultrasound cannot distinguish NASH from simple steatosis 1
When to Upgrade to Advanced Imaging
Consider MRI-PDFF (Proton Density Fat Fraction) when:
You need accurate quantification of liver fat for treatment monitoring or clinical trials 3, 1
MRI-PDFF is the most accurate non-invasive method for detecting and quantifying steatosis, though not recommended as first-line due to cost and limited availability 1
It can map the entire liver for degree of steatosis and is reproducible across different scanners 3, 1
Important caveat: Ensure the MRI uses advanced techniques that correct for confounding factors (T1 relaxation, T2* decay, multi-frequency interference), as conventional MRI without these corrections may be inaccurate and non-reproducible 3, 1
Consider CAP (Controlled Attenuation Parameter) when:
You want simultaneous assessment of steatosis and fibrosis using transient elastography 3, 1
CAP values above 275 dB/m show over 90% sensitivity to detect steatosis 1
The AUC for mild, moderate, and severe steatosis are 0.96,0.82, and 0.70 respectively 1
CAP is promising for rapid, standardized detection but cannot yet be recommended as first-line due to limited availability 1
Practical Algorithm for Clinical Practice
Step 1: Order standard abdominal ultrasound for initial assessment 1, 2
Step 2: Use ultrasound result as binary (present/absent), not for severity grading 3, 1
Step 3: If ultrasound suggests steatosis:
- Calculate NAFLD Fibrosis Score or FIB-4 to assess fibrosis risk 4
- Consider CAP if available for simultaneous steatosis quantification and fibrosis assessment 3, 1
- Reserve MRI-PDFF for cases requiring precise quantification or when monitoring treatment response 3, 1
Step 4: If ultrasound is technically inadequate (common in obesity):
- Proceed directly to MRI-PDFF or CT as second-line imaging 2
Special Considerations for Pediatric Patients
Standard ultrasound remains the screening test of choice alongside ALT in overweight/obese children 3
Available data do not support ultrasound for grading hepatic steatosis in children for clinical care or research 3
MRI shows promise in children but evidence is insufficient for firm clinical recommendations at this time 3
What NOT to Order
Avoid CT for routine NAFLD assessment due to radiation concerns, suboptimal sensitivity for mild steatosis, and interference from iron, copper, or other materials in liver parenchyma 3, 1, 4
Do not order conventional MRI without proper technical specifications for fat quantification, as results may be unreliable 3, 1