A 38-year-old woman with a 10-year history of primary biliary cholangitis (PBC) presents with jaundice, pruritus, and pale stools. Her serum bilirubin is 4.2 mg/dL (predominantly direct), ALP 320 U/L, and ALT 45 U/L. A 42-year-old man with acute viral hepatitis A presents with jaundice, dark urine, and malaise. His serum bilirubin is 6.8 mg/dL (predominantly direct), ALP 95 U/L, and ALT 2200 U/L. Which single feature best distinguishes cholestasis (PBC) from hepatocellular injury (acute hepatitis)?

Explanation

## Distinguishing Cholestasis from Hepatocellular Injury ### Key Biochemical Patterns **Key Point:** The ratio of transaminase elevation to ALP elevation is the most reliable biochemical discriminator between cholestasis and hepatocellular injury. | Feature | Cholestasis (PBC) | Hepatocellular Injury (Acute Hepatitis) | |---------|-------------------|------------------------------------------| | ALT/AST elevation | Mild (< 4× ULN) | Marked (often > 20× ULN) | | ALP elevation | Marked (> 4× ULN) | Mild to moderate (< 4× ULN) | | **ALT:ALP ratio** | **< 1** | **> 1** | | Bilirubin type | Direct predominant | Direct predominant (both can have this) | | Pruritus | Common | Uncommon | | Dark urine | Present (conjugated bili) | Present (conjugated bili) | ### Clinical Pearl **High-Yield:** In cholestasis, ALP rises disproportionately to transaminases because bile duct obstruction or cholestasis induces ALP synthesis from bile duct epithelium. In hepatocellular injury, hepatocyte necrosis releases massive amounts of ALT/AST, while ALP is less dramatically elevated. ### The Discriminator In the case presented: - **PBC (cholestasis):** ALT 45 U/L, ALP 320 U/L → ALT:ALP ratio ≈ 0.14 (cholestatic pattern) - **Acute hepatitis:** ALT 2200 U/L, ALP 95 U/L → ALT:ALP ratio ≈ 23 (hepatocellular pattern) **Warning:** Both conditions can present with direct hyperbilirubinemia and dark urine. Both can cause jaundice. The transaminase-to-ALP ratio is the biochemical signature that separates them. ### Mnemonic **CHOL** = **C**holestasis: **H**igh ALP, **O**wn transaminases **L**ow (relative to ALP) [cite:Harrison 21e Ch 297]