Interpretation of LFTs (Liver Function Tests)

Summary

This video provides a comprehensive guide to interpreting liver function tests (LFTs), focusing on the key components and their significance in diagnosing liver diseases. It explains how various patterns of LFT abnormalities—hepatocellular, cholestatic, isolated hyperbilirubinemia, synthetic dysfunction, and cirrhosis—can indicate different liver or systemic conditions. The video emphasizes the importance of systematic diagnostic approaches, including history review, lab workups, and imaging, to identify common and rare causes of liver dysfunction, helping clinicians refine their diagnosis and treatment strategies.

Takeaways

• 😀 Acute hepatitis can be caused by viral infections, drug toxicity, or ischemia, while chronic hepatitis is often related to ongoing viral infections or alcohol use.
• 😀 A cholestatic liver pattern, characterized by increased bilirubin and GGT, may suggest primary biliary cirrhosis or cholangitis. Further imaging may be needed.
• 😀 Elevated GGT and bilirubin may indicate a cholestatic disorder, while isolated increases in bilirubin require further investigation into potential hemolysis or genetic conditions like Gilbert's syndrome.
• 😀 If GGT is normal but liver enzymes are elevated, bone disease should be considered as a potential cause of the liver dysfunction.
• 😀 In cases of isolated synthetic dysfunction, review the patient's diet and check for proteinuria to rule out malnutrition or nephrotic syndrome.
• 😀 Cirrhosis can result from any untreated chronic liver disease and requires careful screening for hepatocellular carcinoma, including imaging studies like an abdominal CT or ultrasound.
• 😀 The liver function test (LFT) results should always be interpreted in conjunction with the patient's medication and alcohol history, as well as viral hepatitis serologies.
• 😀 A right upper quadrant ultrasound is a crucial diagnostic tool in cases of cholestasis and hyperbilirubinemia, helping to identify obstructive causes or liver masses.
• 😀 For unexplained cases of liver dysfunction, consider rare causes such as autoimmune hepatitis, hemochromatosis, or Wilson's disease, and tailor the workup accordingly.
• 😀 In cases of isolated hyperbilirubinemia, the next step should involve determining whether the bilirubin is unconjugated (indicating hemolysis) or conjugated (suggesting early biliary disease or genetic defects).

Q & A

What are liver function tests (LFTs) used to assess?

Liver function tests (LFTs) are a panel of blood tests used to assess liver function, liver damage, and the integrity of the biliary system, including bile ducts and the gallbladder. They can also provide insights into other physiological aspects such as coagulation, hemolysis, nutrition, and bone turnover.

What are the key components of a standard LFT panel?

The standard LFT panel typically includes four hepatic enzymes: AST (aspartate aminotransferase), ALT (alanine aminotransferase), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT). It also includes tests of synthetic function (albumin and INR) and bilirubin (unconjugated and conjugated).

How do AST and ALT levels indicate liver function?

AST and ALT are transaminases involved in amino acid metabolism. AST is found in various tissues including the liver, heart, and muscle, while ALT is primarily found in the liver. Elevations in these enzymes can indicate liver damage, with ALT being more specific to liver issues. AST is also elevated in conditions like rhabdomyolysis, myocardial infarction, and hemolysis.

What causes an increase in AST and ALT levels?

Increases in AST and ALT can be seen in hepatocellular diseases such as cirrhosis, hepatitis, and drug toxicity. Other causes include fatty liver, congestive heart failure, biliary diseases, and muscle breakdown (rhabdomyolysis). ALT is more specific to liver damage, while AST can also be elevated in non-liver conditions like muscle injury or heart attacks.

What does the AST to ALT ratio indicate in liver diseases?

The AST to ALT ratio is used to help differentiate the cause of liver damage. In alcoholic liver disease, AST typically becomes greater than ALT, especially when cirrhosis develops. A ratio above 2:1 is suggestive of alcohol-related liver disease. A ratio greater than 5 suggests an extrahepatic cause such as rhabdomyolysis or acute myocardial infarction.

What is the significance of alkaline phosphatase (ALP) and GGT in LFTs?

Alkaline phosphatase (ALP) and GGT are markers used to assess biliary function. Elevations in ALP and GGT are seen in biliary diseases such as cholestasis, primary biliary cirrhosis, and cholangiocarcinoma. GGT is more specific for liver disease and is used to differentiate between biliary and bone-related causes of ALP elevation.

What is the role of albumin and INR in liver function tests?

Albumin is a protein produced by the liver, and its levels reflect the liver’s ability to synthesize proteins. A low albumin level suggests chronic liver disease or malnutrition. INR (International Normalized Ratio) measures blood clotting and is influenced by liver function since the liver produces clotting factors. An elevated INR suggests impaired clotting factor synthesis, commonly seen in liver disease.

What can elevated bilirubin levels indicate in an LFT?

Elevated bilirubin levels can indicate liver dysfunction. If both unconjugated and conjugated bilirubin are elevated, it suggests a diffuse hepatocellular or biliary issue. An isolated increase in unconjugated bilirubin can point to hemolysis or genetic conditions like Gilbert’s syndrome. An isolated increase in conjugated bilirubin may indicate early biliary disease or genetic disorders like Dubin-Johnson syndrome.

What is the significance of a high AST and ALT in drug toxicity?

Drug toxicity can lead to significantly elevated AST and ALT levels. Depending on the drug and severity of the reaction, the elevations can range from moderate (200-300 units) to extremely high levels in the thousands. Specific drugs, such as acetaminophen overdose, can cause dramatic increases in AST and ALT.

How can LFTs help diagnose cirrhosis?

In cirrhosis, AST and ALT may be mildly elevated or normal. However, there are more pronounced abnormalities in synthetic tests, such as low albumin and an elevated INR, as well as elevated bilirubin levels. The liver’s inability to synthesize proteins and its dysfunction in processing bilirubin contribute to these LFT changes.