The Fibrotic NASH Index estimates the probability that a fatty liver has already progressed to steatohepatitis with meaningful scarring, from three ordinary blood values — AST, glycated hemoglobin and HDL cholesterol — so what you need is a blood draw at a laboratory, not a scanner and not a biopsy. The condition itself is defined on liver tissue; the index finds who is worth looking at more closely, using labs many adults already have.
"Fibrotic NASH" is a specific target, not a synonym for fatty liver: steatohepatitis active enough to score in the higher range of the standard activity grading, and already at stage 2 fibrosis or beyond. That is the subgroup that tends to progress. Newer papers call it MASH within MASLD.
What you need
- AST (aspartate aminotransferase), in U/L, from a standard liver panel.
- Glycated hemoglobin (HbA1c), as a percentage (NGSP) or in mmol/mol (IFCC).
- HDL cholesterol, from a standard lipid panel, in mg/dL or mmol/L.
- Consistent units — mixing conventions gives a probability that looks reasonable and is wrong.
- Ideally the same laboratory each time; AST assays are not fully harmonized.
Nothing else enters: no age, sex, weight, platelet count or ultrasound. HbA1c needs no fasting; whether the lipid panel does depends on the laboratory. The tests are cheap, but this is a laboratory measurement, not a home one.
How the measurement works
Each input stands in for part of the disease. AST leaks from damaged liver cells and tends to rise relative to the more liver-specific ALT as fibrosis accumulates, so it carries injury and scarring at once. HbA1c summarizes months of blood glucose and marks the insulin-resistant state that drives bland fat toward inflammation. Low HDL belongs to the same picture.
The directions are simple: higher AST and higher HbA1c push the probability up, higher HDL pulls it down. The three are entered on a logarithmic scale, weighted, then passed through a logistic function, so the result is a probability between 0 and 1 and proportional changes matter more than fixed increments.
Enter your three values into the Fibrotic NASH Index (FNI) and let it apply the published transformations, weights and thresholds.
How to read the result
The output is a probability, not a stage and not a diagnosis. The original publication defines two operating points: a low threshold chosen to be highly sensitive, so a value below it makes fibrotic steatohepatitis unlikely, and a higher one chosen to be highly specific. Between them is a grey zone. Read the band the calculator reports, not a decimal quoted without its source.
The rule-out direction is the stronger one: it can tell someone with metabolic risk factors that they probably do not need a specialist workup today. A high result is a trigger for the next test, usually elastography or a referral, not a verdict — and where the condition is uncommon, many high scores are false alarms. If your question is whether fibrosis is already advanced, the FIB-4 Fibrosis Index is the triage tool most guidelines name first.
What it does not tell you
It does not diagnose. Steatohepatitis and fibrosis stage are defined on liver tissue or approximated by imaging; the index only sorts people into worth-investigating and probably-not, and cannot separate stage 2 from cirrhosis. Nor does it establish that there is fat in the liver at all. The Fatty Liver Index (FLI), built from waist circumference, body mass index, triglycerides and GGT, answers that one.
Every input can be moved by something other than the liver. AST rises with alcohol, viral hepatitis and drug-induced injury, and it is not liver-specific: heavy exercise, muscle injury and hemolysis raise it too. HbA1c is unreliable whenever red cells do not live a normal lifespan — anemia, hemoglobin variants, recent transfusion, advanced kidney disease, pregnancy. Treatment moves the inputs too: glucose-lowering therapy lowers HbA1c and fibrates raise HDL, so a score can fall for reasons unrelated to the liver.
Note also where it came from. It was derived in adults with biopsy-confirmed liver disease, and such cohorts are enriched for people sick enough to be biopsied. It is not established for children, in pregnancy, in significant alcohol intake, or alongside another liver disease, and one value on one day is a weaker signal than a trend.
Related reading
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.