Liver Function Test (LFT)

A Liver Function Test (LFT) is a group of blood tests used to measure substances associated with liver-cell activity, bile flow and the liver’s protein-producing function. Depending on the laboratory and the doctor’s request, a panel may include ALT, AST, ALP, GGT, bilirubin, albumin and total protein. Some related tests, such as PT/INR, may be ordered separately when clinically relevant.

The name ‘liver function test’ can be slightly misleading because not every marker directly measures how well the liver is functioning. Some enzymes are better thought of as indicators of cell or bile-duct irritation, while albumin and clotting-related measures can provide different information about protein synthesis. Doctors therefore interpret the overall pattern rather than relying on a single number.

An LFT may be requested when symptoms, medical history, medicines or another test raise a question about liver or biliary health. It may also be used to monitor a known condition or treatment. Reference ranges and panel composition can differ between laboratories, so the values printed on your own report are the correct comparison point.

An LFT is a group of blood measurements used to assess different aspects of liver and biliary function. The panel commonly includes enzymes such as ALT, AST, ALP and sometimes GGT, together with bilirubin, albumin and total protein. These markers do not all mean the same thing: some are more closely related to liver-cell injury, some to bile flow, and others to the liver’s protein-producing function.

Interpretation is therefore pattern based. A rise in ALT and AST has a different clinical meaning from a predominantly raised ALP, while low albumin has a broad differential and may not be caused by liver disease. The exact panel also varies between laboratories, so the included markers on the actual report should be checked before comparing results.

A clinician may request an LFT when evaluating symptoms such as jaundice, persistent upper-abdominal discomfort, unexplained fatigue or changes found on another investigation. It is also commonly used when monitoring known liver disease, viral hepatitis, some medicines that can affect the liver, or metabolic conditions that may be associated with fatty liver. Pre-operative or broader medical assessments can include liver-related tests as well.

The exact reason for testing should guide interpretation. An enzyme pattern that is useful during medicine monitoring may be interpreted differently from the same pattern in a person with acute symptoms.

Liver-panel results are interpreted by looking at the relationship between markers. ALT and AST can rise when liver cells are irritated or injured, while ALP and GGT can be more prominent in some bile-duct or cholestatic patterns. Bilirubin, albumin and total protein provide different information and are interpreted with the rest of the panel.

The degree of an abnormal result does not always correspond directly to the severity or cause of a condition. A clinician may repeat the test or combine it with hepatitis screening, ultrasound or other investigations when appropriate.

An LFT cannot, by itself, identify every liver condition or determine the exact cause of an abnormal result. Normal liver enzymes do not rule out all liver disease, and abnormal enzymes can occasionally reflect non-liver causes. Clinical assessment and, when indicated, additional testing are important.

LFTs use a venous blood sample. Fasting is not always required for an LFT alone, but the laboratory or clinician may request fasting when the test is combined with glucose or lipids. Do not stop prescribed medicines unless instructed by the treating clinician.