The Fibrosis-4 (FIB-4) score is a non-invasive calculation healthcare providers use to estimate the amount of liver scarring, or fibrosis. As a first-line assessment tool, it uses a patient’s age and common lab results to generate a risk value. The primary purpose is to screen patients and sort them into risk categories, guiding clinical decisions. This initial step helps determine the need for referral to a liver specialist, or hepatologist, without requiring immediate invasive procedures like a liver biopsy.
How the FIB-4 Score Is Calculated
The FIB-4 score is calculated using a mathematical formula that incorporates the patient’s age, two liver enzyme levels, and the platelet count. The formula is: (Age [years] x AST [U/L]) / (Platelet Count [10⁹/L] x √ALT [U/L]). This calculation uses readily available information from standard blood tests to produce a score corresponding to a risk level for liver fibrosis.
Age is a factor because the risk of liver fibrosis increases over time. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are enzymes found in the liver. When the liver is damaged, these enzymes can leak into the bloodstream, causing their levels to rise.
Platelets are blood cells that help with clotting. Advanced liver disease, particularly cirrhosis, can lead to a decrease in platelet production and an increase in their destruction, resulting in a lower count. Integrating these four values provides a composite picture that reflects different aspects of liver injury.
Interpreting FIB-4 Score Results
Interpreting the FIB-4 score involves placing the value into one of three risk categories based on numerical cutoffs. These scores represent a risk assessment, not a definitive diagnosis. The results guide the next steps in a patient’s care.
A score below a certain threshold suggests a low risk of advanced liver fibrosis. For individuals under 65, a score of less than 1.3 is generally considered low risk, though some guidelines use 1.45. This result is reliable for ruling out significant scarring, and a patient in this range may not need an immediate specialist referral.
Scores in an intermediate or indeterminate range indicate the risk of advanced fibrosis is unclear. This “gray zone” spans from 1.3 to 3.25 for those under 65. A score in this range is inconclusive and signals the need for additional evaluation.
A high FIB-4 score strongly suggests the presence of advanced liver fibrosis or cirrhosis. A result greater than 3.25 is the high-risk cutoff and is a strong predictor for advanced disease. Individuals with a score in this range should be referred to a liver specialist for further investigation.
Factors That Can Affect Score Accuracy
Several factors can influence the accuracy of the FIB-4 score, with the patient’s age being a significant variable. Because age is a direct component of the formula, the score tends to increase as a person gets older. The standard cutoffs were developed in patient groups that did not heavily feature older adults, making the score less reliable for this demographic.
For patients over 65, the standard low-risk cutoff of 1.3 may not be appropriate, so age-adjusted thresholds are recommended. A higher cutoff, such as less than 2.0, is used to define the low-risk category for this demographic. This adjustment helps avoid misclassifying older adults and prevents unnecessary further testing.
Other conditions can also temporarily affect the laboratory values used in the calculation. For example, acute liver injury or recent heavy alcohol consumption can cause a sharp spike in AST and ALT levels. This inflammation can inflate the FIB-4 score, overestimating the degree of underlying fibrosis.
Next Steps Based on Your Results
The actions taken after receiving a FIB-4 score are tied to the risk category. For individuals with a low-risk score, the result is reassuring, suggesting a low probability of advanced liver fibrosis. The recommendation may be to repeat the score in a few years to monitor for changes and continue managing any underlying conditions.
If the score falls into the indeterminate or high-risk range, it serves as a signal for further action. These results indicate a more detailed evaluation is needed to understand the health of the liver. The most common next step is a referral to a hepatologist, a physician who specializes in liver diseases.
The specialist will likely recommend additional non-invasive tests to get a more precise measurement of liver stiffness. One common follow-up test is transient elastography, known as FibroScan, which uses ultrasound waves to measure scarring. Other imaging studies or blood tests may also be ordered, and in some cases, a liver biopsy may be considered for a definitive diagnosis.