---
title: Liver Function Test Interpretation
description: A comprehensive guide to interpreting common liver function tests in clinical practice.
keywords: [liver enzymes, bilirubin, cirrhosis, hepatitis, cholestasis]
category: clinical
---

## Introduction to Liver Function Tests

Liver function tests (LFTs) are a panel of blood tests used to evaluate the health and function of the liver. The most commonly ordered LFTs include alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), and bilirubin. These biomarkers provide insight into hepatocellular injury, cholestasis, and synthetic liver function. Interpreting LFT patterns can aid in the diagnosis of acute and chronic liver diseases, monitor treatment response, and screen for liver involvement in systemic disorders.

## Patterns of Liver Enzyme Elevations

The pattern of LFT abnormalities can help differentiate the underlying liver pathology:

1. **Hepatocellular injury**: Characterized by predominant elevations in ALT and AST, often >3 times the upper limit of normal (ULN). Common etiologies include viral hepatitis, alcoholic liver disease, and drug-induced liver injury.

2. **Cholestatic injury**: Marked elevations in ALP and GGT, with modest increases in bilirubin. Suggests bile duct obstruction or impaired bile flow, as seen in primary biliary cholangitis, primary sclerosing cholangitis, and drug-induced cholestasis.

3. **Mixed pattern**: Elevations in both hepatocellular (ALT, AST) and cholestatic (ALP, GGT) enzymes. This can occur in conditions like acute hepatitis with cholestatic features, infiltrative liver diseases, and certain drug reactions.

4. **Isolated bilirubin elevation**: Primarily an increase in unconjugated bilirubin, with normal or minimally elevated liver enzymes. This may indicate hemolysis, Gilbert's syndrome, or impaired bilirubin conjugation.

## Interpretation of Common Liver Tests

1. **Alanine Aminotransferase (ALT)**: ALT is a more specific marker of hepatocellular injury, as it is predominantly found in the liver. Elevations are commonly seen in viral hepatitis, alcoholic liver disease, and non-alcoholic fatty liver disease (NAFLD).

2. **Aspartate Aminotransferase (AST)**: AST is also released during hepatocellular damage, but it is less specific as it is also found in other tissues, such as the heart, skeletal muscle, and kidney. The AST/ALT ratio can provide additional clues, with a ratio >2 suggestive of alcoholic liver disease.

3. **Alkaline Phosphatase (ALP)**: ALP is elevated in cholestatic conditions, such as primary biliary cholangitis, primary sclerosing cholangitis, and bile duct obstruction. ALP may also be increased in infiltrative liver diseases, bone disorders, and pregnancy.

4. **Gamma-Glutamyl Transferase (GGT)**: GGT is a sensitive marker of cholestasis and can be used to differentiate the source of ALP elevation (hepatic vs. bone). Isolated GGT elevation may indicate alcohol use or liver enzyme-inducing medication use.

5. **Bilirubin**: Total bilirubin is composed of conjugated (direct) and unconjugated (indirect) fractions. Elevated conjugated bilirubin suggests cholestasis, while unconjugated bilirubin elevation may indicate hemolysis or impaired bilirubin metabolism (e.g., Gilbert's syndrome).

## Approach to Liver Disease Evaluation

When interpreting LFTs, it is essential to consider the clinical context, including the patient's symptoms, medical history, and risk factors. A stepwise approach is recommended:

1. **Identify the pattern of LFT abnormalities**: Determine if the predominant pattern is hepatocellular, cholestatic, or mixed.
2. **Establish the severity of liver injury**: Assess the degree of elevation in liver enzymes and bilirubin.
3. **Consider potential etiologies**: Based on the LFT pattern and clinical presentation, generate a differential diagnosis, which may include viral hepatitis, alcoholic liver disease, NAFLD, autoimmune liver diseases, or drug-induced liver injury.
4. **Order additional tests**: Depending on the suspected etiology, consider serologic tests (e.g., viral hepatitis markers, autoantibodies), imaging studies (e.g., abdominal ultrasound, CT, or MRI), and liver biopsy (if indicated).
5. **Monitor response to treatment**: Repeat LFTs can help assess the effectiveness of interventions and guide further management.

## Chronic Liver Disease and Cirrhosis

In chronic liver diseases, such as cirrhosis, LFT patterns may evolve over time. During the early stages, there may be predominant elevations in hepatocellular enzymes (ALT, AST). As the disease progresses, a more cholestatic pattern (elevated ALP, GGT) may emerge, accompanied by increasing bilirubin levels. The development of portal hypertension and synthetic liver dysfunction can lead to decreases in albumin and prolongation of the prothrombin time (PT)/international normalized ratio (INR).

Monitoring LFTs in cirrhosis is crucial for assessing disease severity and guiding management. The Model for End-Stage Liver Disease (MELD) score, which incorporates creatinine, bilirubin, and INR, is used to prioritize liver transplant candidates and predict short-term mortality risk.

## Considerations for Specific Liver Conditions

1. **Viral Hepatitis**: In acute viral hepatitis (e.g., hepatitis A, B, or C), there is typically a marked elevation in ALT and AST, often >10 times the ULN, accompanied by elevated bilirubin. Chronic viral hepatitis may present with a more moderate elevation in liver enzymes.

2. **Alcoholic Liver Disease**: Characterized by a predominant elevation in AST, often with an AST/ALT ratio >2. GGT is also typically elevated, reflecting both liver injury and alcohol consumption.

3. **Non-Alcoholic Fatty Liver Disease (NAFLD)**: In NAFLD, there is usually a mild to moderate elevation in ALT and AST, with a normal or slightly elevated ALP. The degree of enzyme elevation correlates with the severity of liver fat accumulation and inflammation.

4. **Autoimmune Liver Diseases**: Primary biliary cholangitis (PBC) is characterized by a cholestatic pattern with elevated ALP and GGT. Primary sclerosing cholangitis (PSC) also presents with a cholestatic profile, often with fluctuating liver enzyme levels.

5. **Drug-Induced Liver Injury**: Medication-related liver injury can present with a wide range of LFT patterns, depending on the underlying mechanism. Prompt recognition and discontinuation of the offending drug are crucial.

## Conclusion

Interpreting liver function tests is a crucial skill in clinical practice, as it aids in the diagnosis, monitoring, and management of various liver disorders. By understanding the patterns of LFT abnormalities and their potential etiologies, clinicians can effectively evaluate and manage patients with suspected liver disease.