Diagnosing nonalcoholic fatty liver disease (NAFLD) typically involves a combination of blood tests, imaging, and ruling out other causes of liver fat. There is no single test that confirms it. Instead, doctors work through a step-by-step process: detecting fat in the liver, assessing how much scarring (fibrosis) has developed, and excluding alcohol-related liver disease and other conditions that cause fatty liver. The disease has recently been renamed MASLD (metabolic dysfunction-associated steatotic liver disease), though both terms are still widely used.
Why Diagnosis Isn’t Straightforward
NAFLD is common, affecting roughly one in four adults globally, yet most people with it feel perfectly fine. There are no symptoms in the early stages, and standard blood work can look completely normal. Even when liver enzymes (ALT and AST) are checked, they can fall within the normal range in someone whose liver already has significant fat deposits. In people who do have NAFLD, ALT tends to be higher than AST, but “higher” often still means within the lab’s reference range. This is why NAFLD frequently goes undetected unless a doctor specifically looks for it.
Blood Tests: The Starting Point
Most evaluations begin with a basic metabolic panel and liver function tests. Your doctor will look at ALT and AST levels, which are enzymes released when liver cells are damaged. In NAFLD, ALT is typically greater than AST. But these enzymes alone can’t confirm or rule out the disease. They serve more as a signal that something may warrant further investigation.
Beyond enzyme levels, doctors use simple scoring systems that combine routine lab values to estimate your risk of liver scarring. The most widely used is the FIB-4 score, which factors in your age, ALT, AST, and platelet count. A FIB-4 below 1.3 places you in the low-risk category for advanced fibrosis, meaning you can generally be monitored in primary care. A score of 3.25 or higher signals possible advanced fibrosis and warrants specialist referral. Scores between those two values fall into an indeterminate zone that needs further testing. Because age naturally raises the FIB-4 score, the cutoffs are most reliable for people between 40 and 75.
Another blood-based tool is the Enhanced Liver Fibrosis (ELF) test, which measures proteins involved in scar tissue formation. An ELF score below 9.8 is reassuring, with a 98% chance of ruling out cirrhosis. Scores at or above 9.8 indicate a need for specialist evaluation. Scores of 13 or higher are a red flag: in one study, 80% of people in that range received a clinical diagnosis of cirrhosis.
Imaging: Seeing the Fat and Scarring
Ultrasound is the most common first-line imaging tool. It’s inexpensive, widely available, and can show a bright, echogenic liver characteristic of fat accumulation. The limitation is sensitivity: conventional ultrasound struggles to detect fat when less than about 20% of liver cells are affected, and it can’t reliably measure the exact amount of fat or distinguish mild from moderate steatosis.
FibroScan (transient elastography) is a step up. It provides two measurements in a single, painless session. The Controlled Attenuation Parameter (CAP) estimates fat content in units of dB/m. Values around 236 to 270 dB/m suggest at least mild steatosis, while values above roughly 310 to 340 dB/m point to moderate or severe fat accumulation. The Liver Stiffness Measurement (LSM) estimates fibrosis in kilopascals (kPa). Average readings climb with each fibrosis stage: around 7.5 kPa for no fibrosis, 9.8 for mild, 11.8 for moderate, 15.4 for advanced fibrosis, and 20.3 for cirrhosis. Notably, the cutoffs for fibrosis shift depending on how much fat is present. In livers with less fat, a stiffness reading above 8 kPa suggests significant fibrosis, while in very fatty livers, the threshold rises to about 10.5 kPa.
MRI-based fat quantification (MRI-PDFF) is the most accurate non-invasive method. It can detect liver fat at thresholds as low as 3.7 to 5%, far below what ultrasound picks up. An MRI-PDFF of roughly 5% or more confirms steatosis, with higher percentages corresponding to more severe fat grades: around 17% for moderate and 22% or above for severe. It’s primarily used in research settings or when other imaging gives unclear results, since it costs more and isn’t available everywhere.
Ruling Out Other Causes
NAFLD is, by its original definition, a diagnosis of exclusion. Before confirming it, your doctor needs to rule out other reasons for liver fat. The most important distinction is alcohol intake. The diagnostic threshold is fewer than 30 grams of alcohol per day for men (roughly two standard drinks) and fewer than 20 grams per day for women (roughly one and a half drinks). Drinking above those levels shifts the diagnosis toward alcohol-related liver disease.
Your doctor will also screen for viral hepatitis (particularly hepatitis B and C), autoimmune liver disease, and thyroid disorders. Several medications can cause fatty liver on their own, including corticosteroids, methotrexate, tamoxifen, amiodarone, and certain HIV medications. If you’re taking any of these, the fat in your liver may be drug-related rather than metabolic.
Rarer genetic conditions also mimic NAFLD. These include Wilson’s disease (copper buildup in the liver), lipodystrophy, and inherited disorders of fat metabolism like abetalipoproteinemia and cholesterol ester storage disease. Celiac disease has also been linked to hepatic steatosis. These conditions are uncommon but worth considering, especially if you don’t have the typical risk profile of obesity, type 2 diabetes, or high cholesterol.
The Shift From NAFLD to MASLD
In 2023, an international consensus renamed NAFLD to MASLD. The old name defined the disease by what it wasn’t (not caused by alcohol), while the new name defines it by what it is: fatty liver driven by metabolic dysfunction. Under the MASLD framework, diagnosis requires evidence of liver fat plus at least one of five cardiometabolic risk factors, such as elevated BMI, high blood sugar, high blood pressure, elevated triglycerides, or low HDL cholesterol. In practice, most people previously diagnosed with NAFLD meet MASLD criteria, so the change affects terminology more than it changes who gets diagnosed.
When a Liver Biopsy Is Needed
Liver biopsy remains the gold standard for confirming how much inflammation and scarring are present, but it’s invasive and carries risks like pain, bleeding, and a small chance of serious complications. For most people, non-invasive tests are sufficient. A biopsy is typically reserved for specific situations: when non-invasive scoring falls in the indeterminate range and the clinical picture is unclear, when there’s a strong suspicion of cirrhosis that imaging hasn’t confirmed, when ALT and AST have been persistently elevated for more than six months without explanation, or when another liver disease may be present alongside fatty liver and the doctor needs to sort out the competing diagnoses.
A biopsy can also distinguish simple steatosis (fat without significant inflammation) from steatohepatitis (fat with active inflammation and cell damage), a distinction that non-invasive tests still struggle to make reliably. Steatohepatitis carries a higher risk of progressing to cirrhosis and liver failure, so identifying it can change how aggressively the condition is managed.
What the Diagnostic Process Looks Like in Practice
For most people, NAFLD is discovered incidentally, either through elevated liver enzymes on routine blood work or a bright liver spotted on an ultrasound done for another reason. From there, the typical pathway involves confirming fat is present (usually with ultrasound or FibroScan), running a FIB-4 score to estimate fibrosis risk, and ordering blood tests to rule out hepatitis, autoimmune conditions, and other causes. If your FIB-4 is low and your imaging shows mild fat without significant stiffness, you’ll likely be monitored over time with lifestyle changes as the primary intervention. If scores land in the indeterminate or high-risk zone, you’ll be referred to a hepatologist for further evaluation, which may include an ELF test, MRI-PDFF, or in select cases, a biopsy.
The entire workup can often be completed within a few weeks through your primary care doctor, with specialist referral only when the results suggest more advanced disease. Since NAFLD progresses slowly in most people, the goal of diagnosis isn’t just to label the condition but to identify where you fall on the spectrum, from simple fat accumulation to fibrosis to cirrhosis, so that treatment intensity matches actual risk.