What does it mean if my ALT is higher than my AST?

ALT is found almost exclusively in the liver, while AST is found in the liver, heart, and skeletal muscle. Therefore, an elevated ALT is a much more specific indicator of direct liver injury or inflammation, such as from a viral infection or fatty liver disease.

Why would an AST-to-ALT ratio be greater than 2:1?

While ALT is usually higher in most liver diseases, an AST level that is more than double the ALT level (a ratio > 2:1) is highly suggestive of alcoholic liver disease.

Is high bilirubin always a sign of liver failure?

No. While high bilirubin causes jaundice (yellowing of skin/eyes) and can indicate severe liver disease, mildly elevated bilirubin with normal liver enzymes is often caused by Gilbert's syndrome, a harmless genetic condition where the liver is slightly slow at processing bilirubin.

Liver Function Tests (LFT) Explained — ALT, AST, Bilirubin & More

The Body's Chemical Factory

The liver is the largest internal organ and acts as the body's primary chemical factory. It performs over 500 vital functions, including filtering toxins from the blood, producing bile to digest fats, regulating blood clotting, and storing glycogen for energy. Because it is so critical, doctors use a Liver Function Test (LFT)—also called a Hepatic Panel—to check for liver inflammation, injury, or disease.

What Markers Are Measured?

A standard LFT measures several enzymes and proteins in the blood. When liver cells are damaged, they burst and leak these enzymes into the bloodstream, causing the levels to rise.

1. Liver Enzymes (The Leakage Markers)

ALT (Alanine Aminotransferase): An enzyme found almost exclusively in the liver. It is the most specific marker for liver inflammation or injury.
AST (Aspartate Aminotransferase): An enzyme found in the liver, but also in heart and muscle tissue. It is usually evaluated in comparison to ALT.
ALP (Alkaline Phosphatase): An enzyme found primarily in the bile ducts of the liver and in bone. High levels usually indicate a blockage in the bile ducts rather than damage to the liver cells themselves.

2. Liver Function (The Production Markers)

Bilirubin: A yellowish waste product created when old red blood cells break down. The liver is supposed to process and excrete it. High levels mean the liver isn't clearing it fast enough, leading to jaundice.
Albumin: A protein made exclusively by the liver. It keeps fluid from leaking out of blood vessels. Low albumin levels indicate that the liver has lost its ability to synthesize proteins, a sign of advanced, chronic liver disease.

Interpreting the Results

Normal ranges for ALT and AST are generally less than 40 U/L, though many hepatologists argue the optimal range is less than 30 U/L for men and 19 U/L for women.

Patterns in the bloodwork reveal the type of problem:

High ALT and AST: Indicates hepatocellular injury (damage to the liver cells). Mild elevations (up to 2-3 times normal) are incredibly common and usually point to Non-Alcoholic Fatty Liver Disease (NAFLD) caused by obesity, poor diet, and insulin resistance. Massive elevations (10-20 times normal) indicate acute injury, such as acute viral hepatitis (Hepatitis A, B) or acetaminophen (Tylenol) overdose.
High ALP and Bilirubin: Indicates cholestasis (a blockage of bile flow). This could be caused by gallstones blocking the bile duct, a tumor, or primary biliary cholangitis.

When to Be Concerned

Because the liver has an incredible ability to regenerate, mild, temporary elevations in liver enzymes from a heavy weekend of drinking, a new medication, or a viral infection are common. However, persistently elevated liver enzymes over several months indicate ongoing inflammation that can lead to cirrhosis (permanent scarring). Non-Alcoholic Fatty Liver Disease is rapidly becoming the leading cause of liver failure worldwide, making lifestyle interventions (weight loss, cutting out fructose and alcohol) critical upon seeing elevated ALT/AST levels.

Liver Function Tests (LFT) Explained: ALT, AST, Bilirubin & More