Normal liver enzyme levels fall within a standard range measured in units per liter (U/L) of blood. For the two most commonly tested enzymes, ALT runs from 7 to 55 U/L and AST from 8 to 48 U/L in adult men, though ranges can vary between laboratories and are typically slightly lower for women. If your blood work came back with numbers outside these ranges, understanding what “normal” actually means and how far off your results are matters more than the numbers alone.
The Main Enzymes and Their Ranges
A liver function panel typically measures several markers, each reflecting a different aspect of liver health. The two that get the most attention are ALT and AST, both transaminases that leak into the bloodstream when liver cells are damaged or inflamed.
- ALT (alanine aminotransferase): 7 to 55 U/L. This is the most liver-specific enzyme. It’s found mainly in liver cells, so elevations strongly suggest something is affecting the liver itself.
- AST (aspartate aminotransferase): 8 to 48 U/L. AST is present in the liver but also in heart, muscle, and kidney tissue. An isolated AST elevation without a corresponding ALT rise can sometimes point to damage in those other organs rather than the liver.
These ranges are based on adult men. Women and children often have slightly lower upper limits. Labs set their own reference ranges based on the equipment and methods they use, which is why the “normal” column on your results may differ slightly from the numbers above.
Updated Thresholds for ALT
There’s growing evidence that the traditional upper limits for ALT are too generous. A 2024 study that screened participants without fatty liver or other risk factors for liver disease found that healthier cutoffs were 34 U/L for men and 22 U/L for women. These updated values are noticeably lower than the conventional 55 U/L ceiling many labs still use.
What this means in practice: an ALT of 45 U/L might fall within the “normal” range printed on your lab report but could actually be mildly elevated when compared to people with truly healthy livers. If your ALT consistently sits in the upper portion of the standard range, it’s worth discussing with your doctor, especially if you have risk factors like excess weight or heavy alcohol use.
Other Markers on a Liver Panel
ALT and AST aren’t the only numbers on a liver function test. Your results will likely include several additional markers that reflect different functions.
Albumin is a protein made exclusively by the liver. Normal levels in adults range from 3.5 to 5.5 grams per deciliter. Because the liver produces albumin steadily, a low reading can signal chronic liver problems like cirrhosis, fatty liver disease, or hepatitis. It drops slowly, so it’s more useful for detecting ongoing liver damage than an acute injury.
Alkaline phosphatase (ALP) and bilirubin round out the standard panel. ALP rises when bile flow from the liver is blocked, but it’s also found in bone, so an elevated result doesn’t automatically point to liver trouble. Bilirubin is a yellow pigment processed by the liver. High levels cause jaundice, the yellowing of skin and eyes, and suggest the liver is struggling to clear waste from the blood.
What Counts as a Concerning Elevation
Not all abnormal results carry the same weight. Doctors classify liver enzyme elevations relative to the upper limit of normal (ULN) for your lab, and the degree of elevation changes the urgency.
Mild elevations, defined as less than five times the upper limit of normal, are common in primary care and often turn out to be temporary or related to manageable causes like medication side effects, recent illness, or fatty liver. An ALT of 80 U/L in a lab where the upper limit is 55, for example, would be roughly 1.5 times the ULN, a mild elevation.
Elevations greater than five times the upper limit of normal should prompt immediate evaluation. At that level, something more serious could be happening: acute hepatitis, drug toxicity, or significant bile duct obstruction. An ALT above 275 U/L (five times a 55 U/L ceiling) falls into this category.
Why Your Numbers Might Differ From Someone Else’s
Liver enzyme levels aren’t one-size-fits-all. Several factors shift your baseline independent of liver disease.
Body weight has a strong influence. ALT, AST, and GGT (another liver enzyme) all rise significantly with increasing BMI in both men and women. This relationship is more pronounced in younger adults and tends to be more dramatic in men. Carrying extra weight, particularly around the midsection, promotes fat accumulation in the liver, which drives enzyme levels up even before any symptoms appear.
Sex matters too. Men naturally run higher liver enzyme levels than women, which is why the updated research proposes different ALT ceilings (34 U/L for men, 22 U/L for women). Age also plays a role: the range of enzyme values shifts as you get older, though the direction and magnitude depend on the specific enzyme and your overall metabolic health.
Certain medications can push enzymes up as a side effect. Statins, some antibiotics, anti-seizure drugs, and over-the-counter pain relievers like acetaminophen are well-known culprits. If you’re taking any medications, your doctor should factor that in before interpreting mildly abnormal results.
Preparing for the Test
You’ll typically need to fast for 10 to 12 hours before a liver function test. Water is usually fine, but food and other drinks can affect certain markers, particularly bilirubin and glucose-related values that may be measured alongside the liver panel.
Let your provider know about all medications and supplements you’re taking, since these can influence results. If you’ve been sick recently, some abnormalities may be temporary and resolve on their own. Intense physical exercise can also spike AST (because it’s present in muscle tissue), so a hard workout the day before your blood draw could produce a misleadingly high reading. If your results come back borderline, your doctor may simply retest in a few weeks rather than launching a full workup.
What Abnormal Results Can Mean
Elevated liver enzymes are a signal, not a diagnosis. The most common causes of mild, persistent elevations include non-alcoholic fatty liver disease (by far the most frequent culprit in Western countries), alcohol-related liver damage, viral hepatitis, and medication effects.
The pattern of elevation offers clues. When ALT is higher than AST, viral hepatitis or fatty liver disease is more likely. When AST runs higher than ALT, alcohol-related liver disease or cirrhosis moves up the list. Your doctor will look at the ratio between the two alongside your other lab values and medical history to narrow things down.
Low albumin, on the other hand, suggests the liver has been struggling for a while. Because albumin has a half-life of about three weeks, levels don’t drop quickly. A low reading points toward chronic conditions like cirrhosis rather than a short-term problem.
A single mildly abnormal result on routine blood work isn’t cause for alarm. Many people have transient bumps from a recent illness, a new medication, or even vigorous exercise. What matters is whether the elevation persists on repeat testing and whether other markers on the panel are abnormal at the same time.