NASH FibroSure is a blood test that estimates the degree of liver scarring (fibrosis), fat accumulation (steatosis), and inflammation in people with nonalcoholic fatty liver disease. It uses a panel of common blood markers run through a patented algorithm to generate scores that would traditionally require a liver biopsy to obtain. The test is offered primarily through Labcorp, where it’s listed as NASH FibroSure Plus, while Mayo Clinic Labs offers a similar version called NASH-FibroTest.
What the Test Actually Measures
A standard blood draw collects several biochemical markers. The fibrosis component measures five proteins and enzymes in your blood: alpha-2-macroglobulin, apolipoprotein A1, haptoglobin, total bilirubin, and gamma-glutamyl transpeptidase (GGT). These values are then adjusted for your age and gender and fed into a proprietary algorithm developed by the French company BioPredictive. The algorithm produces a numerical score between 0 and 1 that corresponds to a fibrosis stage.
Beyond fibrosis, the test generates separate scores for steatosis (how much fat is stored in the liver) and for necroinflammatory activity (how much active cell damage and inflammation is occurring). Together, these three scores give your doctor a snapshot of liver health without an invasive procedure.
How Fibrosis Stages Work
The output maps to the METAVIR scoring system, which divides liver fibrosis into five stages:
- F0: No fibrosis
- F1: Mild fibrosis, limited to the portal tracts (the small channels where blood vessels and bile ducts enter the liver)
- F2: Significant fibrosis, with scar tissue starting to bridge between portal tracts
- F3: Severe fibrosis, with extensive bridging but the liver’s overall structure still intact
- F4: Cirrhosis, where scar tissue has fundamentally distorted the liver’s architecture
The distinction between these stages matters because treatment decisions change significantly once fibrosis reaches F2 or higher, and cirrhosis (F4) carries risks of liver failure and liver cancer that require closer monitoring.
How Accurate It Is
A systematic review and meta-analysis published in the Journal of Clinical Medicine pooled data from multiple studies on FibroTest’s performance in fatty liver disease patients. For detecting advanced fibrosis (F3 or higher), the test achieved an area under the curve (AUC) of 0.77, with a sensitivity of 72% and specificity of 69% at the optimal threshold score of 0.30. In plain terms, it correctly identifies about 7 out of 10 people who have advanced fibrosis and correctly rules it out in a similar proportion of people who don’t.
The test performs best at the extremes. For detecting cirrhosis specifically, accuracy jumps to an AUC of 0.92, which is considered excellent. For detecting any fibrosis at all (distinguishing F0 from F1 and above), accuracy drops to an AUC of 0.69, meaning it struggles more with early-stage scarring. This pattern is common across noninvasive fibrosis tests: they’re most reliable when the disease is either clearly absent or clearly advanced, and less precise in the middle stages where clinical decisions are often hardest.
How It Compares to Liver Biopsy
Liver biopsy remains the gold standard for diagnosing NASH and staging fibrosis, but it has real drawbacks. It’s invasive, carries a small risk of bleeding and pain, and samples only a tiny fraction of the liver, which means the results can vary depending on where the needle lands. No imaging method, including ultrasound and MRI, can reliably distinguish NASH (active inflammation with fat) from simple steatosis (fat alone).
NASH FibroSure fills a practical gap: it’s a low-risk screening and monitoring tool that can flag patients who likely need a biopsy while sparing those at lower risk from an unnecessary procedure. However, roughly 25% to 30% of patients tested with noninvasive scoring systems fall into an indeterminate zone where the result isn’t clearly normal or clearly abnormal. For these patients, a biopsy may still be needed to get a definitive answer.
Most of the validation studies for these scoring systems were conducted in Western populations, often in severely obese patients undergoing bariatric surgery. Their accuracy in other populations, particularly those with lower average BMIs, is less well established.
Preparing for the Test
You’ll need to fast for 12 hours before the blood draw. This is important because eating can alter the levels of several markers the algorithm relies on, particularly bilirubin and lipid-related proteins. If your results come back skewed by a recent meal, the fibrosis or steatosis score could be artificially high or low.
Certain medications and medical conditions can also interfere with accuracy. Anything that independently raises or lowers bilirubin, haptoglobin, or GGT in your blood (like hemolytic anemia, Gilbert syndrome, or certain drugs) could affect the result. Your doctor should review your medication list before ordering the test.
Insurance Coverage
Major insurers, including Aetna, consider the FibroTest/FibroSure panel medically necessary for distinguishing cirrhosis from non-cirrhosis in people with chronic liver diseases, including NAFLD and NASH. Coverage typically comes with a few restrictions: most insurers won’t pay for the test more than twice per year, and they won’t cover it if you’ve had a liver biopsy or transient elastography (FibroScan) within the past six months. Using the test for conditions outside of established chronic liver diseases is generally considered experimental and may not be covered.
If you’re uninsured or your plan doesn’t cover the test, expect to pay for a multi-analyte blood panel plus the proprietary algorithm fee. Costs vary by lab, so it’s worth asking Labcorp or your ordering physician’s office for an estimate before the draw.
Where NASH FibroSure Fits in Liver Care
The test is most useful in two scenarios. First, as an initial screen when your doctor suspects fatty liver disease based on elevated liver enzymes, imaging findings, or risk factors like obesity and type 2 diabetes. A low fibrosis score can provide reassurance without the need for a biopsy. Second, as a monitoring tool over time. If you’re making lifestyle changes or receiving treatment, repeating the test every 6 to 12 months can track whether fibrosis is progressing, stable, or improving.
It’s less useful as a standalone diagnostic for NASH itself, since the inflammation and steatosis scores are not as well validated as the fibrosis component. And for patients in the indeterminate scoring range, it may raise more questions than it answers. In those cases, your doctor will likely recommend either a FibroScan (which uses ultrasound waves to measure liver stiffness) or a biopsy to get more definitive staging.