Interpreting LFTs: Hepatitis, Cirrhosis, and Biliary Obstruction

The Two Major Patterns of Liver Injury

Most liver pathologies manifest with a lab pattern that is either predominantly hepatocellular (indicating damage to the liver cells themselves) or cholestatic (indicating a problem with bile flow). Understanding this primary distinction is the first step in your interpretation.

Let's watch a segment from the Strong Medicine video that succinctly defines these patterns.

As the video highlighted, we can summarize the two main patterns like this:

A useful tool to formalize this is the R-value, which compares the relative elevation of ALT to ALP.

$R=\frac{\text{ALT level}/\text{ALT ULN}}{\text{ALP level}/\text{ALP ULN}}$

• R > 5 suggests a hepatocellular pattern.
• R < 2 suggests a cholestatic pattern.
• R between 2 and 5 suggests a mixed pattern.

(ULN = Upper Limit of Normal for your lab)

Now, let's use this framework to examine the three specific clinical scenarios from our learning outcome.

Pattern 1: Acute Hepatocellular Injury (e.g., Acute Viral Hepatitis)

Acute viral hepatitis is a classic example of severe, acute hepatocellular injury. The hallmark is widespread, rapid death of hepatocytes.

The Laboratory Signature

1. Injury Markers (ALT/AST): This is the most dramatic finding. You will see massive elevations of ALT and AST, often greater than 25 times the upper limit of normal, frequently reaching into the thousands ( >1,000 IU/L). In most cases of viral hepatitis, ALT is higher than AST.
2. Synthetic Function (Albumin/INR): Recalling our last lesson, albumin has a long half-life (~20 days), so it will be normal in an acute injury. However, the INR reflects clotting factors with very short half-lives. A rapidly failing liver cannot produce them, so the INR will be elevated (an INR ≥ 1.5 is a defining feature of acute liver failure).
3. Cholestatic Markers (ALP/Bilirubin): These are typically normal or only mildly elevated.

To see how the magnitude of the transaminase elevation provides diagnostic clues, take a look at the following resource.

In summary, the pattern for acute viral hepatitis is:

• ALT/AST >> ALP/GGT (Hepatocellular pattern)
• ALT and AST > 1000 IU/L
• Normal Albumin
• Elevated INR

This combination of a massive transaminase spike with evidence of acute synthetic failure (high INR) but preserved chronic function (normal albumin) is the key signature.

Pattern 2: Chronic Liver Disease (Cirrhosis)

Cirrhosis is the end-stage of any chronic liver disease, characterized by widespread fibrosis and destruction of the normal liver architecture. The lab pattern reflects a long-term, slow decline in liver mass and function.

The Laboratory Signature

1. Synthetic Function (Albumin/INR): This is the defining feature. The failing liver can no longer produce proteins. You will see low albumin and an elevated INR. This is the hallmark of decompensated chronic liver disease.
2. Injury Markers (ALT/AST): These can be surprisingly normal or only mildly elevated. In end-stage cirrhosis, there may be very few healthy hepatocytes left to become inflamed or injured, so the transaminase levels can be deceptively low. An AST:ALT ratio > 2:1 is often seen, especially in alcohol-related liver disease.
3. Cholestatic Markers (Bilirubin): Bilirubin often becomes elevated as the liver loses its ability to conjugate and excrete it, contributing to jaundice.

To reinforce this, let's revisit the Strong Medicine video, which describes this specific "cirrhotic" pattern.

In summary, the pattern for cirrhosis is:

• Low Albumin and High INR (Evidence of chronic synthetic failure)
• Normal or mildly elevated ALT/AST
• Elevated Bilirubin

This pattern of profound synthetic dysfunction in the absence of a dramatic aminotransferase spike points away from an acute process and towards chronic, end-stage disease.

Pattern 3: Biliary Obstruction (Extrahepatic Cholestasis)

Biliary obstruction occurs when something physically blocks the bile ducts outside the liver, such as a gallstone in the common bile duct (choledocholithiasis) or a tumor in the head of the pancreas. This causes bile to back up.

The Laboratory Signature

1. Cholestatic Markers (ALP/GGT/Bilirubin): This is the key abnormality. The pressure buildup in the biliary tree stimulates the cells lining the ducts to produce and release ALP and GGT. You will see a marked elevation in ALP and GGT. Because bile cannot drain, conjugated bilirubin also backs up into the blood, causing a significant conjugated hyperbilirubinemia.
2. Injury Markers (ALT/AST): These are typically normal or only mildly elevated. The back pressure can cause some secondary hepatocyte injury, but it is not the primary process.
   • Clinical Pearl: In acute obstruction (e.g., a passing gallstone), you can see a very brief, sharp spike in ALT/AST right at the beginning, which then falls as the cholestatic markers rise.
3. Synthetic Function (Albumin/INR): This is initially normal. The liver's ability to make proteins is not affected by a simple blockage. However, if the obstruction persists for months or years, it can cause secondary biliary cirrhosis, at which point synthetic function will decline.

The critical next step when you see a cholestatic pattern is to determine where the problem is. Imaging is essential.

As the video explains, a right upper quadrant ultrasound is the crucial next test. The key finding that points to an extrahepatic obstruction is ductal dilation. If the ducts are dilated, it means there is a blockage downstream. If they are not dilated, the problem is more likely intrahepatic (a problem with the microscopic bile ducts within the liver itself).

In summary, the pattern for biliary obstruction is:

• ALP/GGT >> ALT/AST (Cholestatic pattern)
• Markedly elevated ALP, GGT, and Conjugated Bilirubin
• Normal or mildly elevated ALT/AST
• Normal Albumin and INR (initially)

Conclusion

By synthesizing the entire LFT panel, you can identify these classic patterns and narrow your differential diagnosis significantly.

Key Takeaways:

• Acute Viral Hepatitis (Hepatocellular): Characterized by ALT/AST in the thousands, a normal albumin, and a rising INR.
• Chronic Liver Disease (Cirrhosis): Defined by evidence of synthetic failure—low albumin and high INR—with often deceptively mild elevations in ALT/AST.
• Biliary Obstruction (Cholestatic): Marked by significantly elevated ALP, GGT, and conjugated bilirubin, with relatively normal ALT/AST and preserved synthetic function. A cholestatic pattern should always prompt an ultrasound to look for biliary ductal dilation.

You have now completed the module on assessing the liver and biliary system. You have the tools to evaluate liver injury, function, and the flow of bile.

In our next module, we will dive into Coagulation Studies. This is a natural transition, as the INR, a test you now understand as a crucial marker of liver synthesis, is also a central component in assessing the coagulation cascade.