Fatty liver is diagnosed through a combination of blood tests, imaging, and sometimes a specialized scan to check for scarring. Most people discover they have it after routine bloodwork comes back with mildly elevated liver enzymes, or after an ultrasound done for another reason reveals extra fat in the liver. There’s no single test that confirms the diagnosis on its own. Instead, doctors follow a step-by-step process to confirm fat is present, rule out other causes, and determine whether the condition has progressed.
Why the Name Has Changed
If you’ve seen the term NAFLD (nonalcoholic fatty liver disease) before, you’ll increasingly encounter a newer name: MASLD, or metabolic dysfunction-associated steatotic liver disease. Medical organizations moved away from the old terminology because it defined the condition by what it wasn’t (not caused by alcohol) rather than what it was, and because the word “nonalcoholic” was considered stigmatizing. The new name reflects what actually drives the disease: metabolic problems like insulin resistance, obesity, and high blood pressure. The diagnostic approach is essentially the same, but under the updated criteria, a person needs both evidence of liver fat and at least one cardiometabolic risk factor to receive the MASLD diagnosis.
Who Should Be Screened
Not everyone needs testing for fatty liver. Current guidelines recommend screening people at higher risk, particularly those with type 2 diabetes, obesity combined with other metabolic risk factors, or anyone who already has unexplained elevated liver enzymes on routine bloodwork. The American Gastroenterological Association identifies three main groups for screening: people with type 2 diabetes, people with two or more metabolic risk factors, and those who already have an incidental finding of liver fat on imaging or elevated enzymes on blood tests.
The specific cardiometabolic criteria that qualify someone for a MASLD diagnosis include a BMI of 25 or above (23 in Asian populations), fasting blood sugar at or above 100 mg/dL, blood pressure at or above 130/85, triglycerides at or above 150 mg/dL, or low HDL cholesterol (below 40 mg/dL for men, below 50 for women). Meeting just one of these, alongside evidence of liver fat, is enough.
Blood Tests: The First Step
The process typically starts with a standard blood panel that includes liver enzymes, specifically ALT and AST. In fatty liver, these enzymes are usually elevated but not dramatically so, generally less than four times the upper limit of normal. A modest bump in ALT is often the first clue. Doctors also look at the ratio between AST and ALT. When AST is more than double the ALT level, that pattern points more toward alcohol-related liver damage or cirrhosis rather than straightforward fatty liver.
Blood tests alone can’t confirm the diagnosis. Elevated enzymes tell you the liver is stressed but not why. And plenty of people with fatty liver have completely normal enzyme levels. That’s why imaging is the next piece of the puzzle.
At this stage, your doctor will also screen for alcohol use and order tests to rule out other causes of liver damage, such as viral hepatitis, autoimmune conditions, or medications known to cause fat accumulation in the liver. This matters because the diagnosis depends on identifying fatty liver in the absence of these other explanations.
Imaging: Confirming Fat in the Liver
Ultrasound is the most common first-line imaging test. It’s inexpensive, widely available, and involves no radiation. A fatty liver appears brighter than normal on ultrasound because fat reflects sound waves differently. Ultrasound detects moderate to severe fatty liver with about 80% sensitivity and 80% specificity, meaning it catches most cases but can miss mild ones.
MRI is more precise. Standard MRI picks up fatty liver with about 93% sensitivity and 100% specificity. A specialized MRI technique called MRI-PDFF (proton density fat fraction) can actually measure the exact percentage of fat in your liver. A fat fraction of 7% or higher is the sensitive cutoff that flags possible fatty liver, while 12% or higher is used as the more specific threshold that reduces false positives. This test is typically reserved for situations where a precise measurement matters, such as clinical trials or when the diagnosis is uncertain after ultrasound.
CT scans can also detect fatty liver, but they involve radiation exposure and aren’t routinely used for this purpose when ultrasound is available.
Checking for Liver Scarring
Confirming that fat is present in the liver is only half the diagnostic picture. The more important clinical question is whether that fat has caused inflammation and scarring (fibrosis), because that’s what determines your long-term risk. Simple fatty liver without significant scarring is common and relatively benign. Fatty liver with advancing fibrosis can progress to cirrhosis.
The FIB-4 Score
The recommended first-line tool for assessing fibrosis is a simple calculation called the FIB-4 score. It uses your age, platelet count, and AST and ALT levels to estimate your likelihood of significant scarring. No additional tests are needed beyond the bloodwork you’ve already had. A score below 1.30 generally rules out advanced fibrosis with good confidence. A score above 1.30 triggers further evaluation. For people over 65, a higher cutoff of 2.0 is sometimes used because age alone can push the score up.
FibroScan
If your FIB-4 score lands in the intermediate or elevated range, the next step is usually a FibroScan, also called vibration-controlled transient elastography. This is a painless, noninvasive test that takes about 10 minutes. A probe placed against your skin sends a gentle vibration through the liver and measures how stiff the tissue is. Stiffer tissue means more scarring.
Results are measured in kilopascals (kPa). Most healthy people without liver disease score below 7.0 kPa, with the median around 5.3 kPa. A reading above 7 kPa suggests at least significant fibrosis, with about 85% probability. Readings above 14 kPa indicate roughly a 90% chance of cirrhosis. Between 8.0 and 12.0 kPa is considered an indeterminate zone where results may be hard to interpret, and further testing is often needed.
When a Biopsy Is Needed
Liver biopsy remains the gold standard for diagnosing the severity of fatty liver disease, but it’s invasive and carries a small risk of complications. It’s generally reserved for cases where noninvasive tests give conflicting results, when the FibroScan falls in the indeterminate range, or when a doctor needs to distinguish fatty liver from another condition. During a biopsy, a thin needle removes a small sample of liver tissue for examination under a microscope. This can reveal exactly how much fat, inflammation, and scarring are present.
The Diagnostic Pathway Step by Step
Putting it all together, the typical sequence looks like this:
- Step 1: Identify risk. You fall into a screening group because of diabetes, metabolic risk factors, elevated liver enzymes, or incidental findings on imaging.
- Step 2: Initial workup. Blood tests check liver enzymes, and your doctor screens for alcohol use and other causes of liver disease.
- Step 3: Assess fibrosis risk. A FIB-4 score is calculated from your existing bloodwork. If it’s below 1.30, advanced fibrosis is unlikely and you’re monitored over time.
- Step 4: Second-line testing. If the FIB-4 score is 1.30 or above, a FibroScan or similar elastography test measures liver stiffness directly.
- Step 5: Specialist referral. If the FibroScan shows indeterminate results (8.0 to 12.0 kPa) or high stiffness, referral to a liver specialist follows. At that point, a biopsy or MRI elastography may be used to get a definitive answer.
What the Diagnosis Means in Practice
A fatty liver diagnosis isn’t just about the liver. Because MASLD is fundamentally a metabolic condition, the diagnostic process often reveals related problems: prediabetes, high cholesterol, or elevated blood pressure that may not have been caught before. The liver fat itself is a signal that your body’s metabolism is under strain, and the full picture often matters more than any single test result. The degree of fibrosis, not the amount of fat, is what most strongly predicts whether the condition will cause serious health problems down the road.