NAFLD Liver Fat Score (NAFLD-LFS)
NAFLD-LFS (NAFLD Liver Fat Score) is an index that uses metabolic markers to estimate the likelihood of non-alcoholic (metabolic-associated) fatty liver disease. It distills into a single number the presence of metabolic syndrome and diabetes, the level of insulin and liver enzymes — and hints at whether hepatic steatosis is worth looking for.
What NAFLD-LFS is and why it matters
Liver fat accumulates without symptoms for a long time, and the direct ways to see it — ultrasound, elastography, MRI — aren't always at hand at the first visit. NAFLD-LFS (NAFLD Liver Fat Score) is a calculated index that uses routine metabolic measures to estimate how likely non-alcoholic fatty liver disease is. It's a screening tool: it doesn't replace imaging, but it helps work out who needs it first.
The logic of the index is simple: fatty liver disease is closely tied to metabolic dysfunction. So the more pronounced the metabolic syndrome, diabetes, elevated insulin and the characteristic shifts in liver enzymes, the higher the calculated score — and the more likely that fat is already building up in the liver.
NAFLD and steatosis: what they are
Non-alcoholic (metabolic-associated) fatty liver disease (NAFLD) is a chronic liver disease linked to metabolic dysfunction, in which macrovesicular steatosis is found in more than 5% of hepatocytes.
Hepatic steatosis is an accumulation of fat in the liver, in which lipids build up in more than 5% of hepatocytes. It is precisely this fat fraction that NAFLD-LFS tries to predict — not directly, but through the metabolic markers associated with it.
What you need for the calculation
NAFLD-LFS is calculated from five inputs — two yes/no and three laboratory values:
- Metabolic syndrome — yes/no. A cluster of factors (abdominal obesity, elevated blood pressure, blood sugar, disturbed lipids); its presence sharply raises the likelihood of liver fat.
- Type 2 diabetes mellitus — yes/no. An independent risk factor for NAFLD, closely tied to insulin resistance.
- Insulin, mU/L. Fasting insulin reflects insulin resistance — the key mechanism of fat accumulation in the liver.
- AST and ALT, U/L. Liver enzymes; the index uses both the AST level and the AST-to-ALT ratio.
The index combines these inputs into a single score that reflects the likelihood of fatty liver disease. The calculator below does the math correctly — this rules out manual-calculation errors and guarantees fidelity to the original model.
How to prepare for the tests
All three laboratory values come from blood tests. For the result to be correct, it's important to follow the sampling conditions.
Insulin
Taken strictly fasting (8–12 hours without food). Insulin levels are sensitive to recent meals, so a random, non-fasting result will distort the score.
AST and ALT
Part of a standard blood chemistry panel. Take the values and units (U/L) straight from your lab report. The day before, it's best to avoid heavy physical exertion and alcohol, which temporarily raise the enzymes.
NAFLD-LFS Calculator
Indicate whether you have metabolic syndrome and diabetes and enter insulin, AST and ALT — the calculator will compute the NAFLD-LFS index, determine the likelihood of NAFLD and explain the result. The calculation runs on the server.
NAFLD-LFS interpretation threshold (Kotronen et al.): <−0.640 — rules out NAFLD, >−0.640 — indicates probable NAFLD (sensitivity 86%, specificity 71%).
How to read the result
NAFLD-LFS has a single decision threshold — −0.640. It splits the result into two zones.
| Zone | NAFLD-LFS | What it means |
|---|---|---|
| NAFLD unlikely | < −0.640 | Reliably rules out fatty liver disease. |
| NAFLD likely | > −0.640 | Indicates probable NAFLD. A liver ultrasound and other methods are recommended. |
Reliably rules out fatty liver disease.
Indicates probable NAFLD. A liver ultrasound and other methods are recommended.
What each zone means
NAFLD-LFS < −0.640 — NAFLD unlikely
A result below the threshold (sensitivity 86%, specificity 71%) reliably rules out non-alcoholic fatty liver disease. That's a good sign, but not a reason to forget about your metabolism: the index reflects the current picture, and risk factors change over time.
NAFLD-LFS > −0.640 — NAFLD likely
A result above the threshold indicates probable fatty liver disease. This is not a diagnosis but a signal: a liver ultrasound and other diagnostic methods are recommended, along with work on metabolic factors — weight, diet, blood sugar and lipids — together with a physician.
Why metabolic markers predict liver fat
- Insulin resistance. When tissues respond less to insulin, its level rises and the liver stores fat more actively. That's why high fasting insulin is one of the strongest signals in the index.
- Metabolic syndrome. Abdominal obesity, elevated blood pressure, blood sugar and disturbed lipids go hand in hand with liver fat, so its presence noticeably raises the score.
- Type 2 diabetes mellitus. Closely tied to insulin resistance and independently raises the likelihood of NAFLD.
- AST and the AST/ALT ratio. The enzymes reflect the state of liver cells; their level and balance contribute to the final estimate.
NAFLD-LFS combines these signals into a single number, so it performs more accurately than any single measure on its own.
Where it fits in and other indices
NAFLD-LFS is another view of steatosis, one that leans on insulin and the metabolic context. It complements the neighboring tools. FLI and HSI also estimate the likelihood of steatosis, but from other inputs. LAP reflects visceral obesity as the metabolic backdrop. And ANI answers the question of the cause of the damage — alcoholic or metabolic. It's convenient to calculate whichever index you have the labs for and compare the results.
Limitations and important caveats
- It's not a diagnosis. The index estimates the likelihood of NAFLD but does not confirm it — that's done by imaging and a physician.
- It's not a severity assessment. NAFLD-LFS does not measure how much fat is in the liver or whether fibrosis is present.
- Sensitive to sampling conditions. Non-fasting insulin, recent exertion or alcohol distort the result.
- Not about alcohol. The index predicts specifically non-alcoholic disease; to tell the cause apart, use ANI.
- Reflects the current picture. As weight, blood sugar and lifestyle change, the result changes — it makes sense to recompute the index over time.
Frequently asked questions
How does NAFLD-LFS differ from FLI and HSI?
All three estimate the likelihood of steatosis, but from different inputs. What sets NAFLD-LFS apart is that it uses insulin and directly accounts for metabolic syndrome and diabetes — that is, it leans more on the metabolic context. Calculate whichever index you have the labs for.
Do I have to take the insulin test fasting?
Yes. Insulin changes sharply after eating, so only a fasting value (8–12 hours without food) gives a correct score. A random result will overstate the index.
What should I do if the result is above −0.640?
It's a reason to get a liver ultrasound and discuss other diagnostic methods with a physician, as well as to address metabolic factors. A high score on its own is not a diagnosis but an indication of an increased likelihood of fatty liver disease.
Where do I get the metabolic syndrome yes/no?
Metabolic syndrome is diagnosed from a combination of criteria (waist, blood pressure, blood sugar, lipids). If you're not sure, assess them separately: the site has a metabolic syndrome calculator.
Can the index be used with alcohol consumption?
NAFLD-LFS was designed for non-alcoholic liver disease. If the alcohol factor is significant, it's better to clarify the cause with the ANI index and discuss the outcome with a physician.
