The NAFLD Fibrosis Score, usually written NFS, estimates how likely it is that someone with fatty liver disease already has advanced scarring, using six inputs: age, body mass index, whether diabetes or impaired fasting glucose is present, the AST/ALT ratio, platelet count and serum albumin. Four come from a blood draw, so this is not a home measurement, but they are ordinary tests: no scan, no biopsy, no specialist referral.
It was published in 2007 from a cohort with biopsy-confirmed disease and does one narrow job: separating people who almost certainly lack advanced fibrosis from those who probably have it.
What you need
- Your age in years.
- Your height and weight, for body mass index.
- Whether you have type 2 diabetes or impaired fasting glucose: a yes or no input, from a diagnosis or a fasting glucose.
- AST and ALT, from a standard liver panel; the score uses the ratio between them.
- Your platelet count, from a full blood count.
- Your serum albumin, the input most often missing from a basic panel.
Nothing else enters the score. Units are where it goes quietly wrong: the equation expects albumin in g/dL while many labs report g/L, and the wrong unit moves the result more than any real liver change.
How the measurement works
The six values go into a single linear equation, each with a fixed weight. The output is a plain number, positive or negative, read only against two published cut-offs.
Four inputs push the score up: older age, a higher body mass index, diabetes or impaired fasting glucose, and a higher AST/ALT ratio, since AST rising relative to ALT is a long-recognized sign of a liver that is scarring rather than merely fatty. Two push it down: a higher platelet count, because a fibrotic liver and the portal pressure behind it steadily reduce platelets, and higher albumin, since the liver makes it. Rather than reproducing the coefficients by hand, put your six values into the NFS fibrosis score in the units it expects. If albumin was not measured, the FIB-4 Fibrosis Index asks the same question from age, AST, ALT and platelets alone.
How to read the result
| NFS value | Standard reading |
|---|---|
| Below -1.455 | Advanced fibrosis is unlikely; this cut-off exists to rule it out. |
| -1.455 to 0.676 | Indeterminate. The score cannot settle the question either way. |
| Above 0.676 | Advanced fibrosis is likely; clinical assessment and a direct measure of stiffness are the next step. |
The two cut-offs do different jobs, one ruling advanced fibrosis out and one ruling it in, which is why the middle band stays undecided. Below the lower cut-off, advanced scarring is excluded with a negative predictive value close to 90 percent; the price is a gray zone holding roughly a quarter to a third of everyone tested. Overall the score separates advanced from non-advanced fibrosis with an area under the ROC curve in the low 0.8s: enough to triage, not enough to conclude, which is why a high or indeterminate result leads on to Elastography rather than to a decision.
What it does not tell you
NFS does not measure fibrosis. It estimates the probability that a biopsy would show advanced disease and cannot tell the earlier stages apart, so a low result means advanced scarring is improbable, not that your liver is unscarred. It says nothing about fat or inflammation: heavy steatosis with no scarring scores low, correctly.
Age is weighted heavily, and that is its best-known weakness. In adults over about 65 the false-positive rate rises sharply, so a value above the upper cut-off means less at 70 than at 45, and adjusted thresholds have been proposed for that age group. It has never been established for children or pregnancy.
Several inputs move for reasons unrelated to the liver. Platelets fall in marrow disorders and with some drugs; albumin falls in inflammation, kidney protein loss and undernutrition; AST rises after heavy exercise. Each pushes the score toward “advanced fibrosis” in a liver that is fine. It was validated in non-alcoholic fatty liver disease, not in alcohol-related disease or viral hepatitis, and its positive predictive value drops in primary care, where advanced fibrosis is rare. Take any result at or above the lower cut-off to a clinician rather than acting on it alone.
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.