What Are Liver Function Tests?
Liver function tests (LFTs) — also called a hepatic panel — are a group of blood tests that provide information about the health of your liver. They measure enzymes, proteins, and substances that the liver produces or processes. Doctors order LFTs when a patient has symptoms suggesting liver disease, jaundice, exposure to hepatotoxic substances, or as routine monitoring for people on certain medications.
It's important to understand that a single abnormal value rarely tells the whole story. Results are interpreted together, alongside symptoms and imaging findings.
Key Tests in a Standard LFT Panel
1. Alanine Aminotransferase (ALT)
ALT is an enzyme found primarily in liver cells. When liver cells are damaged or inflamed, ALT leaks into the bloodstream, raising its level. ALT is considered the most specific marker of liver cell injury. Elevated ALT suggests hepatitis, fatty liver disease, medication toxicity, or other causes of hepatocellular damage.
2. Aspartate Aminotransferase (AST)
AST is present in the liver, heart, muscles, and kidneys. It is less specific to the liver than ALT. An AST:ALT ratio greater than 2:1 can suggest alcoholic liver disease, while a ratio below 1 is more typical of non-alcoholic fatty liver disease or viral hepatitis.
3. Alkaline Phosphatase (ALP)
ALP is found in the liver, bones, kidneys, and intestines. A raised ALP level often points toward bile duct obstruction or cholestatic liver disease (such as primary biliary cholangitis or gallstones blocking bile flow). It can also be elevated in bone disease, so context matters.
4. Gamma-Glutamyl Transferase (GGT)
GGT is particularly sensitive to alcohol use and bile duct disease. An elevated GGT alongside a raised ALP strongly suggests a biliary or cholestatic cause. GGT can also be raised by certain medications and fatty liver disease.
5. Total Bilirubin
Bilirubin is the yellow pigment responsible for jaundice. The total bilirubin test measures both:
- Direct (conjugated) bilirubin: Processed by the liver. Elevated in obstructive jaundice or hepatocellular disease.
- Indirect (unconjugated) bilirubin: Not yet processed. Elevated in hemolytic anemias or Gilbert's syndrome.
Comparing direct and indirect fractions helps pinpoint where the problem lies in the bilirubin processing pathway.
6. Albumin
Albumin is the main protein made by the liver. A low albumin level reflects impaired synthetic function — the liver's ability to produce proteins — and is associated with chronic liver disease, cirrhosis, or severe malnutrition. It is a marker of long-term liver health rather than acute injury.
7. Prothrombin Time (PT) / INR
The liver produces most clotting factors. A prolonged PT or elevated INR indicates the liver is not producing enough clotting proteins, signaling significant hepatic dysfunction. This test is critical for assessing the severity of liver failure.
How to Read LFT Results: A Quick Reference
| Test | What Elevation Suggests | What Low Levels Suggest |
|---|---|---|
| ALT | Liver cell damage, hepatitis, fatty liver | Generally not clinically significant |
| AST | Liver or muscle damage, alcohol use | Generally not clinically significant |
| ALP | Bile duct obstruction, bone disease | Rarely significant |
| GGT | Alcohol use, bile duct disease | Not clinically meaningful |
| Bilirubin | Jaundice, liver disease, hemolysis | Rarely significant |
| Albumin | Not applicable | Chronic liver disease, malnutrition |
| PT/INR | Clotting disorder, liver failure | Not applicable |
What Happens After Abnormal Results?
Mildly abnormal LFTs are common and may reflect temporary causes such as recent alcohol intake, strenuous exercise, or medications. A single set of results is rarely definitive. Your doctor may:
- Repeat the tests after a few weeks
- Order additional blood tests (hepatitis virus markers, autoimmune antibodies)
- Request imaging studies (ultrasound, CT scan, or MRI)
- Refer you to a hepatologist (liver specialist)
Never interpret LFT results in isolation. Always discuss your results with a qualified healthcare provider who can take your full medical history and symptoms into account.