Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the likely cause of extremely high AST and ALT levels in a patient?

1. Paracetamol overdose

2. Isoniazid toxicity

3. Ethambutol-related issues

4. Rifampin effects

The correct answer is: Paracetamol overdose

Extremely high levels of AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are typically indicative of acute liver injury or damage. Paracetamol overdose is a well-documented cause of such significant elevations in these liver enzymes. When the liver is overwhelmed by excess paracetamol, it can lead to hepatotoxicity, resulting in hepatic cell damage and the release of these enzymes into the bloodstream. This kind of elevation is often seen in the context of overdose due to the metabolism of paracetamol producing toxic metabolites when the available glutathione becomes depleted, leading to increased cellular stress and ultimately necrosis. The levels of AST and ALT can rise to markedly high values, often exceeding a thousand units per liter in severe cases. While other options listed, such as isoniazid toxicity, can also lead to elevated AST and ALT levels, they typically do not reach the extreme heights seen with paracetamol overdose. Ethambutol and rifampin are less likely to cause significant hepatotoxicity compared to the others mentioned in the context of severe elevations. Hence, the association of paracetamol overdose with exceptionally high AST and ALT levels is well-established in clinical practice.