Liver function tests, or LFTs, are one of the most commonly ordered blood panels, yet the numbers can feel confusing at first glance. This guide explains what each value means, how to read the pattern rather than a single number, and the reference ranges to keep in mind. The aim is to make the report easier to understand, not to diagnose any specific case.
This article is educational and does not replace clinical training or advice for a specific patient. All clinical decisions rest with the treating clinician.
What Are Liver Function Tests?
Liver function tests, also called men gan in Vietnamese, are a group of blood markers that reflect the state of the liver and biliary system. Despite the name, they are a mix of enzymes, waste products, and proteins rather than a direct measure of a single function.
The core components are:
- ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes released when liver cells are injured. ALT is more specific to the liver, whereas AST is found in many tissues, so a raised AST alone is less specific.
- ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase) tend to rise when bile flow is impaired. These markers help characterise a cholestatic picture.
- Bilirubin is a breakdown product of red blood cells that the liver processes and clears. Total and direct bilirubin help separate the type of problem.
- Albumin is a protein made by the liver and reflects its synthetic capacity over time. It is one of the true markers of liver function.
How to Read an LFT Report, Step by Step
Reading LFTs is about looking at the pattern across markers, not reacting to a single high value. Here is a systematic way to work through the report.
Step 1: Confirm the reference range for the lab
Reference intervals differ between laboratories and can vary by sex and BMI. Always use the local laboratory reference intervals printed alongside the result, because the same number can be flagged differently across labs.
Step 2: Group the markers into two buckets
Separate the enzymes that signal liver-cell injury (ALT and AST) from the markers that signal impaired bile flow (ALP, GGT, and bilirubin). Reading them as two groups makes the underlying pattern clearer than scanning the list top to bottom.
Step 3: Decide the dominant pattern
ALT and AST elevation out of proportion to ALP and bilirubin suggests a hepatocellular pattern, while ALP and bilirubin predominance suggests a cholestatic pattern. Naming the pattern is the key interpretive step, since it points the clinical reasoning in different directions.
Step 4: Check the AST to ALT ratio
When the transaminases are the main abnormality, look at their ratio. An AST to ALT ratio of at least 2 to 1 suggests alcohol-associated liver disease. This is a supporting clue that is interpreted together with the rest of the picture, not a stand-alone diagnosis.
Step 5: Read albumin as a longer-term signal
Albumin reflects the synthetic function of the liver. Because it turns over slowly, it speaks to a more chronic state rather than an acute event.
Normal Reference Values
The table below lists adult reference ranges from the provided source material. These values vary by lab, sex, and BMI, so treat them as orientation and defer to the local report.
| Marker | Adult reference range | Source |
|---|---|---|
| ALT | 4 to 36 IU/L | Reference |
| AST | 5 to 30 IU/L | Reference |
| ALP | 30 to 120 IU/L | Reference |
| GGT | 6 to 50 IU/L | Reference |
| Total bilirubin | 2 to 17 micromol/L | Reference |
| Direct bilirubin | 0 to 6 micromol/L | Reference |
| Albumin | 35 to 50 g/L | Reference |
Ranges vary by laboratory and by sex, so the numbers above are a general reference only.
Common Mistakes When Reading LFTs
- Reacting to one number instead of the pattern. A single flagged value means less than how the markers move together. The hepatocellular versus cholestatic distinction comes from the overall pattern.
- Treating AST as liver-specific. AST is found in many tissues, while ALT is more specific to the liver, so an isolated AST rise should not be read as liver-only.
- Ignoring the local reference interval. Using a generic range instead of the local laboratory reference intervals can misclassify a normal or abnormal result.
- Overlooking albumin. Albumin reflects synthetic function and adds context that transaminases alone do not provide.
When to Escalate to a Clinician
LFTs are a screening and monitoring tool, not a substitute for clinical judgement. Any interpretation of an abnormal result, choice of further testing, or decision about treatment belongs with the treating clinician who knows the full history and examination. If a report shows a pattern you do not understand, or values outside the local reference range, the right next step is to bring it to a qualified clinician rather than acting on the numbers alone. As stated above, all clinical decisions rest with the treating clinician.
Reading LFTs With Phở
Phở is built as a calm, cited workspace for clinical and research questions. When you ask about a lab pattern, its Clinical Answer Mode grounds the response in retrieved literature and keeps the sources visible next to each claim, so you can inspect where a statement comes from. Where the evidence does not support a claim, Phở labels it rather than guessing. The tool is meant to help you read and reason, and the interpretation of any real patient result still rests with the treating clinician.