A liver blood test is most commonly called a liver function test, or LFT. You may also see it referred to as a liver panel, liver function panel, liver profile, or hepatic function panel. Several of these markers are also included in a comprehensive metabolic panel (CMP), which is one of the most routinely ordered blood tests, so you may have had some liver values checked without even realizing it.
Despite the name, a liver function test doesn’t measure a single thing. It’s a group of individual tests run from one blood draw, each looking at a different enzyme or protein to build a picture of how well your liver is working and whether it’s been damaged.
What a Liver Panel Measures
A standard liver panel typically includes the following markers:
- ALT (alanine transaminase): An enzyme concentrated in liver cells that helps convert proteins into energy. When liver cells are injured, ALT leaks into the bloodstream, so elevated levels are one of the most specific signs of liver damage. You may see this listed as SGPT on older lab reports.
- AST (aspartate transaminase): An enzyme that helps break down amino acids. It’s present in the liver but also in muscle tissue, so a high AST level can point to liver damage or muscle injury. Sometimes labeled SGOT.
- ALP (alkaline phosphatase): An enzyme found in the liver and bones. Elevated ALP often signals a problem with bile flow, such as a blocked bile duct, but it can also rise with certain bone conditions.
- GGT (gamma-glutamyl transferase): Another enzyme tied to bile duct function. GGT is most commonly elevated due to obesity, excess alcohol consumption, or certain medications. When ALP is high, GGT helps clarify whether the cause is liver-related or coming from somewhere else, like bone.
- Bilirubin: A yellow waste product created when your body breaks down old red blood cells. The liver processes bilirubin so it can be excreted in stool. High bilirubin can indicate liver disease or a blockage in the bile ducts, and it’s the substance responsible for jaundice (yellowing of the skin and eyes).
- Albumin and total protein: Albumin is a protein manufactured by the liver that helps fight infections and carry substances through the bloodstream. Low albumin or total protein levels suggest the liver isn’t producing proteins the way it should, which can occur with chronic liver disease or cirrhosis.
- Prothrombin time (PT): This measures how long your blood takes to clot. The liver makes prothrombin and other clotting factors, so a longer-than-normal clotting time can be a sign of liver damage.
- LDH (lactate dehydrogenase): An enzyme found throughout the body, with some of the highest concentrations in the liver. It’s a less specific marker but adds context when other values are abnormal.
What Each Marker Tells You
These tests fall into a few categories based on what part of liver health they reflect. ALT and AST are considered liver injury markers. They sit inside liver cells and are released when those cells are damaged, so elevated levels often appear before you have any symptoms at all. ALT is more liver-specific, while AST can also rise after intense exercise or muscle injury, which is why doctors look at both numbers together.
ALP, GGT, and bilirubin are grouped as cholestatic markers, meaning they reflect problems with bile flow. When ALP and GGT are both elevated, the pattern points toward a bile duct issue, whether from gallstones, a stricture, or inflammation of the bile ducts themselves. An isolated ALP elevation, without a corresponding rise in GGT, is more likely related to bone rather than liver.
Albumin, total protein, and prothrombin time measure the liver’s synthetic function, its ability to manufacture the proteins and clotting factors your body depends on. These markers tend to stay normal in early or mild liver disease and drop only when the liver has sustained significant, often chronic, damage. Low albumin paired with a prolonged clotting time is a pattern that raises concern for advanced liver disease.
Why Your Doctor May Order One
Liver panels are ordered for a wide range of reasons. Sometimes they’re part of routine bloodwork, bundled into a comprehensive metabolic panel during an annual physical. Other times, a doctor orders one because of specific symptoms like unexplained fatigue, abdominal pain in the upper right side, dark urine, pale stools, nausea, or yellowing of the skin.
You’re also more likely to have a liver panel ordered if you take medications that can stress the liver (including common over-the-counter pain relievers), drink alcohol regularly, have a family history of liver disease, or have conditions like obesity or diabetes that increase the risk of fatty liver disease. If you’ve already been diagnosed with a liver condition, repeat panels help track whether the problem is stable, improving, or getting worse.
How the Test Works
A liver panel requires a simple blood draw, usually from a vein in your arm. The process takes a few minutes, and results are typically available within a day or two. Many liver function tests are included within a comprehensive metabolic panel, so if your doctor orders a CMP, you’ll automatically get several liver values without needing a separate test.
Fasting isn’t always required, but some labs or doctors may ask you to fast for 10 to 12 hours beforehand, particularly if other tests are being run at the same time. It’s worth asking when you schedule the blood draw. Alcohol, certain supplements, and medications can all affect results, so mention anything you’re taking.
What Abnormal Results Mean
A single abnormal value doesn’t necessarily mean you have liver disease. ALT and AST can temporarily spike from a vigorous workout, a recent illness, or even certain herbal supplements. GGT is sensitive to alcohol, so a few drinks in the days before the test can push it above normal range. ALP naturally runs higher in children and teenagers because their bones are still growing.
Patterns matter more than individual numbers. Elevated ALT and AST together suggest liver cell injury from causes like viral hepatitis, fatty liver disease, or medication toxicity. Elevated ALP and GGT together point toward a bile flow problem. Low albumin with prolonged clotting time suggests the liver has lost significant function over time.
When results come back abnormal, the next step usually involves repeat testing to confirm the finding, additional blood work (like hepatitis screening or iron studies), or imaging such as an ultrasound to look at the liver’s structure. One abnormal liver panel is a starting point for investigation, not a diagnosis on its own.