Hepatic Steatosis Index (HSI)
HSI (Hepatic Steatosis Index) is a non-invasive screening index that estimates the probability of non-alcoholic (metabolic dysfunction-associated) fatty liver disease from two liver enzymes and simple body measurements. You need ALT, AST, BMI, sex and information about diabetes mellitus.
What HSI is and why it's needed
HSI (Hepatic Steatosis Index) is a simple calculated measure that uses a routine biochemical blood test and body data to estimate how likely fat accumulation in the liver is. Its value lies in requiring neither an ultrasound nor expensive tests: two liver enzymes, height, weight, sex and an answer about diabetes are enough.
Like other indices of this kind, HSI is a screening tool, not a diagnosis. It doesn't "see" the liver or measure the amount of fat in it directly. Its job is to sort: who can confidently have fatty liver disease ruled out, and who should undergo further examination. This is exactly how it is used in clinical research and in large-scale screening.
Steatosis, NAFLD and MASLD — what they are
Hepatic steatosis is the accumulation of fat in the liver cells (hepatocytes). Steatosis is diagnosed when fat is present in more than 5% of hepatocytes. At this stage the changes are still reversible.
Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease associated with metabolic dysfunction, in which macrovesicular steatosis is present in more than 5% of hepatocytes and there is no significant alcohol use as a cause. Today this condition is increasingly called metabolic dysfunction-associated steatotic liver disease (MASLD) — the new name more accurately reflects its link to excess weight, insulin resistance and metabolic syndrome. HSI was created specifically as a screening tool for NAFLD/MASLD.
What you need for the calculation
HSI is calculated from several inputs. Two of them are liver enzymes from a biochemical blood test; the rest are simple facts about you:
- ALT (alanine aminotransferase), U/L. An enzyme that resides inside liver cells and enters the blood when they are damaged.
- AST (aspartate aminotransferase), U/L. The second enzyme; it is the ratio of ALT to AST that carries information about the nature of liver damage.
- Body mass index (BMI). Calculated automatically from the height and weight you enter — no need to input it separately.
- Sex. Factored into the index, because in fatty liver disease the values differ between men and women.
- Presence of diabetes mellitus. Diabetes is closely linked to fatty liver disease and increases the risk.
The index combines liver enzymes, body mass index, sex and diabetes status into a single measure of fatty liver disease risk. The calculator below performs the calculation correctly — this eliminates manual arithmetic errors and guarantees fidelity to the original model.
How HSI differs from FLI
HSI and FLI (the Fatty Liver Index) address the same task — steatosis screening — but rely on different inputs. That's convenient: you can compute whichever index you have the lab work for.
| Parameter | HSI | FLI |
|---|---|---|
| Enzymes | ALT and AST | GGT |
| Blood lipids | — | Triglycerides |
| Anthropometry | BMI | BMI and waist circumference |
| Additional factors | Sex, diabetes | — |
ALT + AST + BMI + sex + diabetes. A good fit when basic biochemistry (transaminases) is available but triglycerides and GGT are not.
GGT + triglycerides + BMI + waist circumference. A good fit when a lipid profile and GGT are available.
How to measure correctly
The accuracy of HSI depends on the accuracy of your data. Take ALT and AST from your biochemical blood test report, and measure height and weight under the same conditions each time.
Height
Measure without shoes, standing straight, heels together, gaze horizontal.
Weight
Weigh yourself on the same scale, ideally in the morning, on an empty stomach, in light clothing or without it — that keeps results comparable across repeat measurements.
HSI Calculator
Enter your values — the calculator computes the hepatic steatosis index, determines the zone and explains the result. The calculation runs on the server; the model coefficients are not sent to the browser.
HSI interpretation thresholds (Lee et al., 2010): <30 — NAFLD can be ruled out, 30–36 — indeterminate, >36 — high probability of NAFLD.
How to read the result
The HSI scale is divided into three zones by two thresholds. Between "can be ruled out" and "highly likely" there is a range that is more honestly called indeterminate.
| Zone | HSI | What it means |
|---|---|---|
| NAFLD ruled out | < 30 | Fatty liver disease can be ruled out. |
| Indeterminate | 30–36 | NAFLD can be neither confirmed nor ruled out — a gray zone. |
| High probability | > 36 | NAFLD is highly likely — further evaluation is recommended. |
Fatty liver disease can be ruled out.
NAFLD can be neither confirmed nor ruled out — a gray zone.
NAFLD is highly likely — further evaluation is recommended.
What each zone means
HSI < 30 — NAFLD can be ruled out
A value below 30 reliably rules out fatty liver disease. That's no reason to relax forever, but it is a reason not to worry now: it's enough to maintain your weight, diet and activity and repeat the assessment at your routine check-up.
HSI 30–36 — an indeterminate result
The "gray zone": NAFLD is possible, but the index cannot say for certain. The right next step is to weigh the result against other factors and, if needed, undergo a liver ultrasound. The decision is made by a physician.
HSI > 36 — a high probability of NAFLD
A value above 36 indicates a high probability of fatty liver disease. It is neither a verdict nor a measure of severity: the index does not distinguish simple steatosis from inflammation and does not measure fibrosis. But it is a strong reason to show the result to a physician, undergo further evaluation and address the modifiable factors — weight loss, diet, physical activity. At an early stage, steatosis is reversible.
Why these particular inputs
- The ALT/AST ratio. Both enzymes reflect the state of the liver cells, but their balance changes predictably in fatty liver disease — which is why the index uses the ratio rather than the individual values.
- BMI. A general measure of excess body weight, which is closely tied to steatosis risk.
- Sex. Fat distribution and metabolism differ between men and women, and all else being equal the risk differs too — so the index includes a correction for sex.
- Diabetes mellitus. Diabetes and insulin resistance are among the main drivers of fat accumulation in the liver, so its presence raises the final estimate.
Limitations and important caveats
- This is not a diagnosis. HSI estimates only the probability of steatosis and does not replace ultrasound, elastography or biopsy.
- It does not measure severity. The index does not distinguish simple steatosis from steatohepatitis and does not assess fibrosis.
- A "gray zone" is normal. A result of 30–36 is not an error but an honest signal that a closer look is needed.
- It can be distorted. Acute liver disease, certain medications and comorbidities can shift the enzyme levels.
- Context matters more than a single number. HSI is interpreted together with your history, lifestyle and other lab results — and this is done by a physician.
What to do with the result
- Green zone (<30): maintain your lifestyle, keep an eye on your weight, and repeat the assessment at routine check-ups.
- Yellow zone (30–36): discuss with your doctor whether a liver ultrasound and a check of metabolic factors are warranted.
- Red zone (>36): show the result to your doctor, undergo further evaluation and actively work on the modifiable factors — weight loss, diet, activity and cutting out excess alcohol.
Early steatosis is reversible: for many people, moderate weight loss reduces the amount of fat in the liver. But the specific plan for examination and action should be drawn up by a physician — do not order tests or treat yourself on your own.
Frequently asked questions
Do I need to enter BMI separately?
No. Enter your height and weight — the body mass index is calculated for you. That's more reliable than plugging in BMI by hand.
Which should I choose — HSI or FLI?
Both estimate the probability of steatosis, but from different inputs. Compute whichever index you have the lab work for: for HSI you need ALT and AST, for FLI — GGT and triglycerides. You can compute both and compare.
Does HSI > 36 mean I have cirrhosis?
No. A high HSI indicates only a high probability of steatosis — fat accumulation. This is an early and often reversible stage; it is not the same as cirrhosis. The index does not assess fibrosis or disease severity.
Why are sex and diabetes part of the calculation?
Because with the same enzymes and BMI the risk of fatty liver disease differs between men and women, and having diabetes raises it. These corrections are built into the model to make the estimate more accurate.
Can I track changes over time with HSI?
Yes — if the index falls as you lose weight, that's a good sign. But decisions about diagnosis and treatment are based on direct investigations, not on the index trend alone.
