FIB-4

Serum (preferred) or plasma and whole blood

1 mL (serum or plasma); fill tube to capacity (whole blood)

0.5 mL (serum or plasma); 0.5 mL (whole blood)

Gel-barrier tube or red-top tube or green-top (heparin) tube or lavender-top (EDTA) tube (plasma), and a separate lavender-top (EDTA) tube (whole blood)

FIB-4 index is reported to be a simple, accurate, non-invasive, and readily available laboratory test index that can help in evaluation of patients with HCV and Non-Alcoholic Fatty Liver Disease (NAFLD), now known as Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), for the presence of liver fibrosis indication for liver biopsy and other liver-related complications. It was also reported to be concordant with FibroSure test results.

Clumping may cause false low platelet count. Platelet satellitism around neutrophils will cause a pseudothrombocytopenia. RBC or WBC fragments including fragmented fragile leukemic cells and neutrophil pseudoplatelets may cause falsely elevated counts.

AST and ALT: Kinetic

Platelet Count: Automated cell counter

0 – 1.29: low risk for advanced liver fibrosis

1.30 – 2.67: Indeterminate risk for advanced liver fibrosis

>2.67: high risk for advanced fibrosis and for developing of other liver-related events

The FIB-4 index value is calculated using the 4 parameters formula:

FIB-4 = [Age(Years) x AST (IU/L)] / [Platelets (10E3/L) x ALT^.5 (IU/L)]

The FIB-4 index was reported in a study of patients with HCV infection to correctly identify patients with severe fibrosis (METAVIR F3-F4) with area under the ROC curve of 0.85. A FIB-4 index of less than 1.45 had a negative predictive value of 94.7% to exclude extensive fibrosis (F3-F4) with a sensitivity of 74.3% and a specificity of 80.1%. A FIB-4 index of greater than 3.25 had a positive predictive value of 82.1% to confirm the existence of significant fibrosis (F3-F4) with a specificity of 98.2% and a sensitivity of 37.6%. In the same study, FIB-4 index was in agreement with FibroTest (known in the US as FibroSure) test results of 92.1% for exclusion of severe fibrosis (F3-F4) using a cutoff of less than 1.45, and agreement of 76.0% for detection of severe fibrosis (F3-F4) using a cutoff of greater than 3.25.

In more recent studies of patients with NAFLD, FIB-4 index was reported to have area under ROC curve of 0.802 for prediction of advanced fibrosis (F3-F4)using slightly different cutoffs of 1.30 and 2.67. A negative predictive value for the absence of advanced fibrosis at a cutoff of 1.30 was 83% and a positive predictive value for the presence of advanced fibrosis and hazard ratio for developing liver realated events at a cutoff of 2.67 was 80% and 14.6 respectively. A liver biopsy had been appropriately avoided in 54% of cases.