Liver Function TestsEdit
Liver function tests (LFTs) are a common set of blood measurements used to assess the health and performance of the liver. They help clinicians screen for liver disease, investigate symptoms such as jaundice or fatigue, monitor known liver conditions, and guide treatment decisions. LFTs reflect hepatocellular integrity, biliary excretion, and the liver’s synthetic capacity, but they are not disease-specific and can be influenced by a range of factors outside the liver itself.
A liver function test panel typically includes measurements of enzymes, pigments, and proteins that together paint a picture of liver function. Interpretation depends on patterns across several values rather than a single number, and results are influenced by laboratory methods, age, medications, and comorbidities. In clinical practice, LFT results are integrated with history, physical exam, imaging, and sometimes noninvasive tests of fibrosis or, rarely, biopsy to establish a diagnosis.
Common tests included in a liver function test panel
- ALT (alanine aminotransferase) and AST (aspartate aminotransferase): enzymes released from hepatocytes when cells are damaged; elevations suggest hepatocellular injury.
- ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase): enzymes associated with bile ducts; elevations can indicate cholestasis or biliary obstruction, though ALP can also rise with bone disease.
- Total bilirubin (bilirubin) and direct bilirubin (direct bilirubin): bilirubin is a pigment processed by the liver; elevations may reflect impaired conjugation, cholestasis, or increased red blood cell turnover.
- Albumin (albumin) and PT/INR (international normalized ratio or prothrombin time): measures of the liver’s synthetic function; low albumin or a prolonged INR can occur in chronic or advanced liver disease.
- Additional tests occasionally used in the workup: LDH (lactate dehydrogenase) and, in some panels, other markers. More specialized assessments may include bilirubin fractions or tests of bile acids.
Patterns of abnormality and what they suggest
- Hepatocellular pattern: ALT and/or AST are disproportionately elevated relative to ALP; this pattern points toward hepatocyte injury from viral hepatitis, drug-induced liver injury (drug-induced liver injury), alcohol-related liver disease, or other inflammatory or toxic processes.
- Cholestatic pattern: ALP and GGT are elevated with or without bilirubin elevation, indicating problems with bile formation or flow, such as biliary obstruction, primary biliary cholangitis, or certain drug-induced cholestasis.
- Mixed pattern: Concurrent elevations in hepatocellular and cholestatic markers can occur with more complex disease or multifactorial liver injury.
Interpreting LFTs also requires considering the duration and magnitude of abnormalities, as well as accompanying clinical features, imaging findings, and fibrosis assessments when available. Patterns may be influenced by age, sex, pregnancy, medications, alcohol use, and comorbid conditions such as congestive heart failure or metabolic disease.
Indications and clinical uses
- Evaluation of jaundice, fatigue, right upper quadrant pain, or abnormal screening tests.
- Baseline and safety monitoring before and during therapies known to affect the liver (for example, certain antibiotics, antiepileptics, statins, or medications with hepatic metabolism).
- Monitoring chronic liver diseases such as viral hepatitis, nonalcoholic fatty liver disease (nonalcoholic fatty liver disease), or cirrhosis, to gauge progression or response to treatment.
- Preoperative risk assessment and general medical evaluation where liver function may influence management.
- Guiding further testing, including targeted imaging, hepatitis panels, autoimmune evaluation, or fibrosis assessment.
Limitations, variability, and controversies
- Non-specificity: LFTs do not pinpoint a diagnosis on their own. Abnormal results require correlation with history, exam, imaging, and sometimes liver biopsy to determine cause.
- Normal results do not exclude disease: people with fatty liver disease or chronic liver injury can have near-normal LFTs, especially in early stages.
- Pre-analytical and analytical variability: results can differ between laboratories due to assay methods, reference ranges, and handling of specimens; clinicians interpret results within the context of the specific lab report.
- False positives and incidental findings: mild transaminase elevations may be transient or related to recent exercise, medications, or alcohol; this can lead to unnecessary testing if not interpreted judiciously.
- Screening debates: routine LFT screening in asymptomatic individuals is not universally recommended, because many abnormalities are incidental and may lead to further testing without clear benefit in some populations. Focused, risk-based testing and targeted evaluation often provide a more efficient approach.
- Role of fibrosis and noninvasive testing: while LFTs are part of the initial assessment, increasingly clinicians use noninvasive fibrosis scores (for example, FIB-4 score or NAFLD fibrosis score) and imaging techniques like transient elastography (transient elastography) to assess liver scarring more directly. In some cases, liver biopsy (liver biopsy) remains the reference standard to define certain conditions.
- Complex interpretations in multisystem disease: conditions outside the liver (such as congestive heart failure or hemolysis) can alter LFTs, which can complicate the diagnostic pathway and require broader clinical consideration.