Liver Function Tests – Values and Meaning
Liver function tests are blood tests used to assess the health and function of the liver. They help detect and monitor liver diseases at an early stage.
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Liver function tests are blood tests used to assess the health and function of the liver. They help detect and monitor liver diseases at an early stage.
What Are Liver Function Tests?
Liver function tests (LFTs) are a group of blood tests that provide information about the condition and function of the liver. They are routinely ordered as part of a blood panel and play a key role in medical diagnostics. Abnormal liver values may indicate diseases of the liver, bile ducts, or other organs.
Key Liver Parameters Explained
ALT (Alanine Aminotransferase)
ALT is an enzyme found primarily in liver cells. Elevated ALT levels indicate liver cell damage, such as that seen in hepatitis, alcohol-related liver disease, or medication-induced liver injury.
AST (Aspartate Aminotransferase)
AST is found in the liver as well as in heart and muscle cells. Elevated AST levels may point to liver cell damage, but can also be associated with heart attacks or muscle disorders.
GGT (Gamma-Glutamyltransferase)
GGT is a sensitive marker for liver damage, especially related to chronic alcohol use or bile duct disorders. It can also be elevated due to certain medications.
ALP (Alkaline Phosphatase)
Alkaline phosphatase (ALP) is an enzyme found in the liver, bones, kidneys, and intestine. In liver diagnostics, it is mainly used as an indicator of bile duct disease or bone metabolism disorders.
Bilirubin
Bilirubin is a breakdown product of hemoglobin (the red blood cell pigment). The liver is responsible for processing and excreting bilirubin. Elevated bilirubin levels may manifest as jaundice (icterus) and can indicate liver dysfunction, bile duct obstruction, or excessive breakdown of red blood cells.
Albumin
Albumin is a protein produced exclusively by the liver. Low albumin levels indicate impaired liver function and are commonly seen in chronic liver diseases such as liver cirrhosis.
Prothrombin Time (PT) / INR
The prothrombin time (PT) and its standardized form, the INR, measure blood clotting ability. Since many clotting factors are produced in the liver, a prolonged PT or elevated INR is a sign of severe liver dysfunction.
Reference Ranges and Normal Values
Normal reference ranges may vary slightly between laboratories, and also depending on age and sex. Typical reference values for adults are:
- ALT: up to 35 U/L (women), up to 45 U/L (men)
- AST: up to 35 U/L (women), up to 50 U/L (men)
- GGT: up to 40 U/L (women), up to 60 U/L (men)
- ALP: 35–105 U/L (adults)
- Total bilirubin: 0.2–1.2 mg/dL
- Albumin: 3.5–5.0 g/dL
- Prothrombin time (Quick): 70–130%
Any deviations from these ranges should always be evaluated in the context of clinical findings and other diagnostic results.
Causes of Abnormal Liver Values
Elevated liver enzyme levels can have many causes, including:
- Viral liver infections (Hepatitis A, B, C)
- Alcohol-related liver damage
- Fatty liver disease (non-alcoholic fatty liver disease, NAFLD)
- Medication side effects (e.g., paracetamol/acetaminophen, statins)
- Autoimmune hepatitis
- Bile duct obstruction or gallstones
- Liver cirrhosis
- Liver cancer or metastases
- Heart failure (congestive hepatopathy)
When Should Liver Values Be Tested?
Testing liver function is recommended in the following situations:
- Regular or excessive alcohol consumption
- Use of medications known to affect the liver
- Existing liver disease or a family history of liver conditions
- Symptoms such as fatigue, yellowing of the skin or eyes (jaundice), upper abdominal pain, or dark urine
- Routine health check-ups
- Obesity or metabolic syndrome
Diagnosis and Interpretation
Liver test results must always be interpreted by a physician within the broader clinical context. A single mildly elevated value does not necessarily indicate disease. A pattern of multiple abnormal parameters, combined with clinical symptoms, medical history, and further investigations (e.g., liver ultrasound, liver biopsy), enables a reliable diagnosis.
Treatment for Abnormal Liver Values
Treatment depends on the underlying cause and may include:
- Abstaining from alcohol and making lifestyle changes
- Weight loss in cases of fatty liver disease
- Adjusting or discontinuing liver-damaging medications
- Antiviral therapy for viral hepatitis
- Specific treatment for autoimmune hepatitis, bile duct disease, or other identified causes
References
- European Association for the Study of the Liver (EASL): Clinical Practice Guidelines on the Management of Hepatitis. Journal of Hepatology, current edition. www.easl.eu
- Kasper, D.L. et al. – Harrison's Principles of Internal Medicine. McGraw-Hill Education, current edition.
- World Health Organization (WHO): Hepatitis – Global Health Sector Strategies. www.who.int
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