Enzimas Hepáticas Para que sirven en Medicina ALT y AST?

Key Concepts

• Aspartate aminotransferase (AST): An enzyme primarily found in the liver mitochondria.
• Alanine aminotransferase (ALT): An enzyme primarily found in the liver cytoplasm.
• Hepatitis: Inflammation of the liver.
• Alcoholic hepatitis: Liver inflammation caused by excessive alcohol consumption.
• Viral hepatitis: Liver inflammation caused by a viral infection.
• Autoimmune hepatitis: Liver inflammation caused by the body's immune system attacking the liver.
• Cirrhosis: Scarring of the liver.
• Fatty liver disease: Accumulation of fat in the liver.
• Fulminant hepatic failure: Rapid onset of severe liver dysfunction.
• Ischemia: Insufficient blood supply to the liver.
• Necrosis: Death of liver tissue.
• Acetaminophen toxicity: Liver damage caused by excessive acetaminophen intake.

1. AST and ALT Enzymes in Liver Diagnosis

• The video focuses on using AST and ALT levels to differentiate between various liver conditions.
• AST is located in the mitochondria of liver cells, while ALT is located in the cytoplasm.
• When the liver is inflamed, these enzymes leak into the bloodstream, elevating their levels.

2. Alcoholic Hepatitis

• Alcohol is a mitochondrial toxin.
• In alcoholic hepatitis, AST levels are typically higher than ALT levels (AST > ALT).
• The mnemonic "vodka starts with S, so AST" is used to remember the association between alcohol and AST elevation.

3. Hepatitis with Cellular Damage

• In most hepatitis cases with cellular damage, ALT levels are higher than AST levels (ALT > AST).
• This is because ALT is primarily located in the cytoplasm, which is more readily affected by general liver cell damage.

4. Normal Enzyme Levels

• Normal AST levels are less than 40 units per liter.
• Normal ALT levels are less than 50 units per liter.

5. AST/ALT Ratio and Liver Conditions

• Calculating the AST/ALT ratio can help determine the cause of liver damage.
• Enzyme levels of 500 or less are often seen in:
  • Cirrhosis
  • Chronic viral hepatitis
  • Fatty liver disease
  • Alcoholic hepatitis (sometimes)

6. Acute Hepatitis and Autoimmune Hepatitis

• Enzyme levels between 500 and 1000 suggest:
  • Acute hepatitis
  • Autoimmune hepatitis
• Viral hepatitis typically presents with enzyme levels above 500, often in the thousands (e.g., 2000-4000).

7. Fulminant Hepatic Failure

• Enzyme levels near or above 10,000 indicate a fulminant cause, such as:
  • Ischemia (e.g., due to shock)
  • Severe toxicity (e.g., acetaminophen overdose)
• Ischemia can lead to necrosis if not addressed quickly.

8. Acetaminophen Toxicity Example

• Acetaminophen overdose is given as an example of a severe toxicity that can cause fulminant hepatic failure.

9. Differential Diagnosis Based on Enzyme Levels

• AST > ALT: Suggests alcoholic hepatitis.
• ALT > AST: Suggests hepatitis with general cellular damage.
• < 500: Cirrhosis, chronic viral hepatitis, fatty liver disease.
• 500-1000: Acute hepatitis, autoimmune hepatitis.
• > 10,000: Fulminant hepatic failure (ischemia, severe toxicity).

10. Conclusion

The video provides a practical guide to using AST and ALT levels to quickly differentiate between common liver conditions. By considering the relative levels of AST and ALT, their absolute values, and the clinical context, clinicians can narrow down the possible diagnoses and guide further investigations and treatment. The video emphasizes the importance of considering alcoholic hepatitis, viral hepatitis, autoimmune hepatitis, cirrhosis, fatty liver disease, and fulminant hepatic failure in the differential diagnosis of liver disease.