Liver function tests, what you have to know

Liver function tests Overview

The liver has many vital functions, ranging from storage and metabolism to detoxification, secretion, and excretion. With this vital role of the liver, it is important to ensure that all its functions are properly functioning by monitoring each function through a specific test. An abnormal result, higher or lower than the normal value, could indicate the presence of a problem with the liver. Total protein, Albumin, Prothrombin time, Alkaline phosphatase (ALP), Aspartate aminotransferase (AST), Alanine transaminase (ALT), Gamma-glutamyl transferase (GGT), Bilirubin, and Lactate dehydrogenase are among the most commonly requested liver function tests. In this article, we will discuss liver functions, laboratory tests for liver functions, and their normal values.

Liver Functions

The liver, the largest solid organ in the body, performs many vital functions that include detoxication, metabolic, hemostatic, and others. Liver functions can be classified into the following categories:

1- Detoxication: it filters the blood to remove toxins.
2- Metabolism of fats and carbohydrates
3- Hemostatic function regulation blood clotting
4- Production of bile which is essential for vitamin absorption. Also, it produces plasma proteins, such as albumin, and clotting factors.
5- Excretion of bilirubin, cholesterol, hormones, and drugs.
6- Storage of glycogen, vitamins, and minerals
7- Immunological Functions: The liver contains Kuffer cells involved in immune activity. These destroy any disease-causing agents.

Liver Function Tests Classification

A- Tests for Synthetic Function

• Total Protein: This test measures the total amount of protein in the blood and assesses if there is any severe condition associated with the liver. Normal Value for Total Protein: 6.5-8.3 g/dL It’s increased in Malignancy, Multiple myeloma, Waldenstrom’s macroglobulinemia Decreased in Hepatic cirrhosis, Glomerulonephritis, Nephrotic syndrome, Starvation
  • Albumin, Globulin, and A/G Ration
    Normal Value for Albumin: 3.5-5 g/dL

• Prothrombin Time

B- Synthesis and Excretion Function Tests

• Bilirubin: It is a waste product made by the liver. Bilirubin results from hemoglobin metabolism. There 2 types of Bilirubin; conjugated and unconjugated.
  – Jaundice or hyperbilirubinemia, also known as icterus, is the yellow coloration of the skin when blood bilirubin exceeds 2-3 mg/dL

C- Tests for Detoxification Function and excretory functions

• Serum bilirubin, Unconjugated (indirect) or Conjugated (direct). Increased Conjugated bilirubinemia can be seen in biliary tract disease but can also be elevated in hepatocellular conditions. Elevation of unconjugated bilirubin rarely is due to liver disease.
• Urine bilirubin. All bilirubin in urine is conjugated.
• Blood ammonia is usually converted to urea by the liver. It’s increased in liver diseases. Normal Value for Ammonia: 11-35 mmol/L or 19-60 ug/dL
• Aminotransferases, AP, 5′-nucleotidase, and GGT

• Enzyme tests
  • ALP: (alkaline phosphatase), It is an enzyme found in the liver and bone. It is important for proteins metabolism. High levels occur in liver damage or certain bone diseases.
  • ALT: (alanine transaminase), ALT is a liver enzyme that helps convert proteins into energy for the liver cells. When the liver is damaged, ALT is released, and levels increase.
  • AST: (aspartate aminotransferase) It is an enzyme for amino acid metabolism. It is normally present in blood at low levels and increases due to liver damage.
  • 5′ nucleotidase
  • GGT
  • OCT
  • LAP
  • LDH: Lactate dehydrogenase, an enzyme found in most of the body’s cells. It is released into the blood when cells have been damaged by disease or injury.

Elevated liver enzymes

Elevated liver enzymes may be a sign that the liver is not working properly, where damaged or inflamed liver cells release enzymes into the bloodstream, that will be elevated, which a blood test can detect.

The most common cause of elevated liver enzymes is fatty liver disease. 25–51% of people with elevated liver enzymes have fatty liver diseases, as reported by studies. Other health conditions that usually cause elevated liver enzymes include:

• metabolic syndrome
• hepatitis
• alcohol or drug use disorder
• cirrhosis, which is liver tissue scarring

Other conditions that may, (less commonly), cause elevated liver enzymes include:

• autoimmune hepatitis
• celiac disease
• infection with the Epstein-Barr virus.
• liver cancer
• hemochromatosis, when the body absorbs too much iron
• mononucleosis
• sepsis, or blood poisoning
• Wilson’s disease
• polymyositis, which involves inflammation of the muscles
• Certain medications, including some pain relievers and statins, can also cause elevated liver enzymes.

SUMMARY

Liver function tests will help us to know the status of the liver, and whether it is functioning normally or not. There is a wide variety of tests that must be within the normal range. Blood tests for liver function test include ALT (7 to 55 units per liter), AST (8 to 48 U/L), ALP (40 to 129 U/L), Total protein (6.3 to 7.9 g/dL), Albumin (3.5 to 5.0 g/dL), Bilirubin (0.1 to 1.2 mg/dL), GGT (8 to 61 U/L), LD (122 to 222 U/L), PT (9.4 to 12.5 seconds) and others.

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SOURCES

• https://byjus.com/biology/liver/
• Mayo Clinic
• Elevated liver enzymes: Causes, symptoms, tests, and treatment (medicalnewstoday.com)
• Mildly Elevated Liver Transaminase Levels: Causes and Evaluation | AAFP
• Liver Function Tests: Types, Purpose & Results Interpretation (clevelandclinic.org)
• Liver Function Tests: Purpose, Procedure, and Results (healthline.com)
• https://medlineplus.gov/lab-tests/liver-function-tests/