What it measures: fibrosis
Who should take it: anyone concerned about their liver
Where to get it: primary care provider, online calculator
The FIB-4 Index is a blood-based diagnostic test that looks at underlying fibrosis that can be used as a measure to help determine NAFLD/NASH status. While originally developed to detect liver fibrosis among patients with Hepatitis C and HIV, FIB-4 scoring has been increasingly used by the diabetes and NAFLD/NASH communities.   The FIB-4 scoring system is determined from the values of patient age, platelet count, aspartate aminotransferase (AST), and alanine aminotransferase (ALT). As all of these tests are available to primary care physicians, FIB-4 is a highly accessible and affordable screening tool. A sample report can be seen below:
In clinical trials for NAFLD/NASH diagnosis, patients with a FIB-4 score <1.3 were classified as not having advanced fibrosis, while patients with a FIB-4 score >2.67 were classified as having advanced fibrosis. Those with FIB-4 scores 1.3-2.6 were indeterminate, requiring further testing. As a test to rule out advanced fibrosis (FIB-4 <1.3), FIB-4 has a negative predictive value of 90-95%. This means that 90-95% of those identified as not having advanced fibrosis truly do not have advanced fibrosis, while the remaining 5-10% are false negatives requiring further validation. As a test to rule in advanced fibrosis (FIB-4 >2.6), FIB-4 has a positive predictive value of 80%. This means that 80% of those identified as having advanced fibrosis truly have advanced fibrosis, while the remaining 20% are false positives requiring further validation.
Unlike some other tests, FIB-4 looks solely at fibrosis, not taking into consideration other factors important for diagnosis and monitoring of NAFLD/NASH such as steatosis and activity. While it is fairly limited in this sense, the high accuracy in detection of fibrosis makes it a strong starting point for NAFLD/NASH diagnosis that can help the right patients get on track for further testing and treatment. As all of these tests are readily available to primary care physicians, FIB-4 is a highly accessible and affordable screening tool. If you have your platelet count, AST, and ALT values from a previous bloodwork, you can enter them yourself in the calculator here:
 Shah et al., USE OF THE FIB4 INDEX FOR NON-INVASIVE EVALUATION OF FIBROSIS IN NONALCHOLIC FATTY LIVER DISEASE, Clinical Gastroenterology and Hepatology, October 2009, doi: 10.1016/j.cgh.2009.05.033.