A standard liver function test (often called an LFT or liver panel) is a group of blood tests that measure specific enzymes, proteins, and waste products to reveal how well your liver is working. The panel typically includes ALT, AST, ALP, GGT, bilirubin, albumin, total protein, and prothrombin time. Each marker tells a slightly different story about liver health, from cell damage and bile flow to the liver’s ability to make essential proteins.
What a Standard Liver Panel Includes
When your doctor orders a liver function test, you’re not getting a single measurement. It’s a collection of tests run from one blood draw, each targeting a different aspect of liver health. The results fall into three broad categories: enzymes that signal cell damage, waste products that reflect how well the liver processes and clears substances, and proteins that show whether the liver is manufacturing what your body needs.
The enzymes measured are ALT (alanine transaminase), AST (aspartate aminotransferase), ALP (alkaline phosphatase), and GGT (gamma-glutamyl transferase). Your liver cells contain these enzymes in high concentrations, and when cells are injured or inflamed, the enzymes leak into your bloodstream. Higher-than-normal levels are often the first clue that something is off.
The panel also measures bilirubin, a yellowish waste product created when your body breaks down old red blood cells. Your liver is responsible for processing and removing most bilirubin. Albumin and total protein round out the panel by showing how well the liver is producing key proteins. Finally, prothrombin time (PT) measures how quickly your blood clots, since the liver makes most of the proteins involved in clotting.
ALT and AST: Markers of Liver Cell Damage
ALT and AST are the two enzymes most closely tied to liver cell injury. ALT is found almost exclusively in the liver, which makes it a more specific indicator of liver problems. AST is also present in the heart, muscles, and kidneys, so an elevated AST alone doesn’t always point to the liver.
When both enzymes are elevated, the ratio between them can offer diagnostic clues. In alcohol-related liver disease, about 90% of patients have AST levels more than double their ALT levels. This pattern occurs because alcohol depletes a vitamin the liver needs to produce ALT and simultaneously causes the type of cell damage that releases extra AST. An AST-to-ALT ratio greater than 2 strongly suggests alcohol as a factor. In non-alcoholic causes of liver disease, ALT is usually higher than AST, at least until significant scarring develops. Once cirrhosis sets in from any cause, AST tends to overtake ALT, though the gap is less dramatic than in alcohol-related cases.
ALP and GGT: Bile Duct Health
ALP and GGT are especially useful for detecting problems with bile flow. Bile is a digestive fluid produced by the liver and stored in the gallbladder. When bile ducts become blocked or inflamed, both ALP and GGT rise.
ALP has a quirk: it’s also found in bone, so elevated ALP on its own could signal a bone condition rather than a liver problem. That’s where GGT becomes the tiebreaker. If both ALP and GGT are elevated, the issue is almost certainly liver or bile duct related. If ALP is high but GGT is normal, the source is more likely bone.
Bilirubin: Processing and Clearance
Bilirubin results are reported in up to three forms: total, direct, and indirect. Total bilirubin combines the other two. Normal total bilirubin is about 1.2 mg/dL in adults and 1 mg/dL in children. Jaundice, the visible yellowing of skin and eyes, typically appears when total bilirubin climbs above 3 mg/dL.
Direct bilirubin (also called conjugated) is the form your liver has already processed into a water-soluble version for removal through bile. Normal direct bilirubin is around 0.3 mg/dL. When direct bilirubin is elevated, it usually means the liver is struggling to clear bilirubin properly, pointing toward liver damage, liver disease, or a blocked bile duct.
Indirect bilirubin (unconjugated) is the form that hasn’t yet been processed by the liver. High indirect bilirubin can signal problems occurring before the liver’s involvement, such as excessive breakdown of red blood cells.
Albumin and Prothrombin Time: Synthetic Function
While enzymes and bilirubin reveal damage and blockages, albumin and prothrombin time show whether your liver can still do its manufacturing job. This distinction matters because a liver can be inflamed yet still functioning, or it can be so scarred that it can no longer produce what the body needs.
Albumin is the most abundant protein the liver makes. It helps maintain fluid balance in your blood vessels and carries hormones and nutrients throughout the body. Because albumin has a long half-life of two to three weeks, it drops slowly and is most useful for detecting chronic liver problems rather than acute ones. A low albumin level in the context of liver disease suggests the liver has been underperforming for a sustained period.
Prothrombin time works on a faster timeline. Clotting factors produced by the liver have shorter half-lives than albumin, so PT responds more quickly to both sudden and long-term liver failure. A prolonged PT (meaning your blood takes longer to clot) indicates the liver isn’t making enough clotting proteins. This makes PT valuable for catching acute liver injury as well as monitoring chronic disease.
The FIB-4 Score: Estimating Liver Scarring
Beyond the standard panel, doctors sometimes calculate a FIB-4 score to estimate how much scarring (fibrosis) exists in the liver. This isn’t a separate blood draw. It uses four values you may already have: your age, AST level, ALT level, and platelet count.
A FIB-4 score below 1.45 has a 90% chance of correctly ruling out advanced fibrosis. A score above 3.25 is 97% specific for advanced fibrosis. In the original study that validated this formula, about 70% of patients fell clearly into one of these two categories, meaning they could potentially avoid a liver biopsy based on blood work alone, with an overall accuracy of 86%.
Why Your Doctor Might Order a Liver Panel
Liver panels are ordered for a wide range of reasons. Common triggers include unexplained fatigue, abdominal pain (especially in the upper right side), yellowing of the skin or eyes, dark urine, nausea, and swelling in the legs or abdomen. They’re also ordered routinely to monitor known conditions like hepatitis, fatty liver disease, or cirrhosis, and to check for liver side effects when you’re taking certain medications.
Risk factors that may prompt screening even without symptoms include heavy alcohol use, obesity, diabetes, a family history of liver disease, and long-term use of medications known to stress the liver.
Medications and Supplements That Affect Results
More than 1,000 drugs have been linked to liver injury, so elevated enzymes on a liver panel don’t always mean you have liver disease. Common over-the-counter culprits include ibuprofen (Advil, Motrin) and naproxen (Aleve), especially with frequent use or when combined with alcohol. Acetaminophen (Tylenol) is safe at recommended doses but is the most common cause of acute liver failure in overdose.
Prescription medications that can raise liver enzymes include certain antibiotics, antiseizure drugs, immunosuppressants, antifungals, and anabolic steroids. Herbal supplements are responsible for roughly 20% of drug-induced liver injury cases in the United States. Products containing green tea extract, kava kava, kratom, turmeric supplements, black cohosh, and valerian are among those most frequently implicated. If you’re getting a liver panel, mention every supplement you take, not just prescription medications.
Preparing for the Test
A liver panel requires a simple blood draw, usually from a vein in your arm. Whether you need to fast depends on context. If the liver panel is part of a comprehensive metabolic panel, fasting for 10 to 12 hours is typically required. If it’s ordered on its own, your doctor may not require fasting at all. Ask when the test is scheduled.
Let your provider know about all medications, vitamins, and supplements you’re taking beforehand. Some may need to be paused, but don’t stop any prescription medication unless specifically told to do so.