Liver Function Tests and Aminotransferases Quiz

Liver Function Tests

• Liver function tests (LFTs) are a group of blood tests that assess liver function and identify liver damage or disease by measuring levels of proteins, enzymes, and waste products in the blood.

• Albumin is the main protein produced by the liver, and total protein measures the combined amount of albumin and globulin.

• Alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyl transferase (GGT), bilirubin, and lactate dehydrogenase (LD or LDH) are also included in LFTs.

Aminotransferases

• Aminotransferases catalyze amino group transfer (transamination) from an amino acid to a keto acid, crucial for amino acid metabolism and the urea cycle.

• All aminotransferases require pyridoxal-5-phosphate (PLP) (vitamin B6) as a coenzyme.

Alanine Aminotransferase (ALT)

• ALT, also known as SGPT, is a cytoplasmic enzyme predominantly located in the liver, released when the cell membrane is damaged.

• It's a highly specific marker for liver disease and present in high amounts in the liver and kidney, with minimal amounts in the heart and skeletal muscle.

• ALT plays a significant role in the tricarboxylic acid cycle (TCA cycle) or Krebs cycle, catalyzing the interconversion of alanine and α-ketoglutarate to pyruvate and glutamate.

ALT Normal Values

• Female: 7-30 IU/L (0.12-0.50 µkat/L)

• Male: 10-55 IU/L (0.17-0.91 µkat/L)

Factors Affecting ALT Levels

• Liver diseases like hepatitis, alcoholic liver disease, non-alcoholic fatty liver disease (NAFLD), and cirrhosis.

• Hemolysis of the blood sample.

• Numerous medications can increase ALT levels, including ACE inhibitors, acetaminophen, anticonvulsants, heparin, lipid-lowering agents, thiazides, and antibiotics.

Elevated ALT Levels May Indicate

• Alcoholic liver disease
• Liver cancer
• Biliary obstruction
• Hepatitis or inflammation of the liver
• Use of medicines or drugs toxic to the liver
• Cirrhosis

Aspartate Transaminase (AST)

• AST, or SGOT, is an enzyme that exists in two forms: cytoplasmic (AST1) and mitochondrial (AST2).
• AST is present in all body tissues, with the highest activity found in the liver, heart, skeletal muscle, and erythrocytes.
• AST reflects damage to hepatic cells but is less specific for liver disease than ALT.
• AST helps diagnose various heart, muscle, or brain disorders like a myocardial infarction, obstructive jaundice, acute hepatic necrosis, and malignant disease.

AST Normal Values

• Female: 9-25 IU/L (0.15-0.42 µkat/L)
• Male: 10-40 IU/L (0.17-0.67 µkat/L)
• Elderly: Slightly higher norms
• Newborn: Norms two to three times higher than adults.

Factors Affecting AST Levels

• Acute renal disease
• Liver cancer
• Cirrhosis
• Hepatitis
• Liver necrosis
• Muscle inflammation
• Biliary obstruction

AST/ALT Ratio

• The AST/ALT ratio helps differentiate liver disease causes.

• A ratio less than one (ALT higher than AST) suggests non-alcoholic fatty liver disease.

• A ratio equal to one (ALT equal to AST) suggests acute viral hepatitis or drug-related liver toxicity.

• A ratio greater than one (AST higher than ALT) suggests cirrhosis.

• A ratio greater than 2:1 (AST more than twice as high as ALT) suggests alcoholic liver disease.

Alkaline Phosphatase (ALP)

• ALP is an enzyme found in various parts of the body, including the liver, bones, intestine, placenta, and kidneys.

• It's a hydrolase enzyme responsible for removing phosphate groups from molecules (dephosphorylation).

• ALP functions include protecting the intestinal tract, aiding in digestion, breaking down fats and some B vitamins, promoting bone formation, as well as contributing to nucleic acid and protein synthesis.

• ALP is used as a tumor marker that increases in cases of osteogenic sarcoma and metastatic bone cancers.

ALP Normal Values

• Female: 30-100 IU/L (0.5-1.67 µkat/L)
• Male: 45-115 IU/L (0.75-1.92 µkat/L)
• Elderly: Slightly higher norms
• Children: One to three times adult norms
• Pregnancy: Two to three times adult norms

Factors Affecting ALP Levels

• Hemolysis of the blood sample.
• Medications like estrogen, lipid-lowering agents, antibiotics, heparin, and salicylates can increase ALP levels.
• Medications like cyanides, oxalates, zinc salts, and propranolol can decrease ALP levels.

Elevated ALP Levels May Indicate

• Liver disease
• Bone disease
• Pregnancy
• Biliary obstruction
• Hepatitis
• Leukemia
• Vitamin D deficiency
• Cirrhosis
• Liver cancer
• Pancreatitis

Decreased ALP Levels May Indicate

• Celiac disease
• Excessive vitamin D intake
• Malnutrition
• Anemia
• Hypothyroidism
• Chronic nephritis