What is IQR FibroScan?
IQR (Interquartile Range) in FibroScan is a quality control metric that measures the variability between individual liver stiffness measurements, and a result is only considered technically reliable when the IQR is less than 30% of the median value. 1, 2
Technical Definition and Purpose
- The IQR represents the statistical spread of the 10 individual liver stiffness measurements obtained during a FibroScan examination 2
- It is calculated as the difference between the 75th and 25th percentile values of all valid measurements 1
- The IQR/median ratio serves as a quality indicator to ensure measurement consistency and reproducibility 1
Validity Criteria for FibroScan Results
A FibroScan result meets technical validity requirements only when ALL three criteria are satisfied: 2, 3
- ≥10 successful measurements obtained 2, 3
- Success rate ≥60% 2, 3
- IQR <30% of the median value (when reported in kPa) 1, 2
For measurements reported in meters per second (m/s), the IQR should be less than 15% of the median 1
Clinical Significance of IQR
- High IQR values (≥30%) indicate unreliable measurements that should not be used for clinical decision-making, as they suggest excessive variability between individual readings 1, 2
- Common causes of elevated IQR include patient movement during the procedure, inadequate fasting (less than 4 hours), obesity, narrow intercostal spaces, or operator inexperience 1
- When IQR criteria are not met, the examination should be repeated or alternative assessment methods (such as MR elastography or liver biopsy) should be considered 1
Practical Application
- The FibroScan device automatically calculates and displays the IQR alongside the median liver stiffness value 1
- Clinicians must verify that the IQR/median ratio is <30% before interpreting the liver stiffness measurement for staging fibrosis 2, 3
- Results failing IQR criteria should be documented as "technically inadequate" rather than reporting an unreliable numerical value 1
Common Pitfalls to Avoid
- Never rely on a FibroScan result with IQR ≥30%, even if the median value appears clinically plausible 1, 2
- Ensure patients fast for at least 4 hours before testing, as postprandial blood flow falsely elevates both liver stiffness values and IQR 3
- In obese patients (BMI >28 kg/m²), consider using the XL probe, which may improve success rates and reduce IQR 1
- Active hepatic inflammation, acute hepatitis, extrahepatic cholestasis, and right heart failure can elevate both liver stiffness and IQR independently of fibrosis 1