Final answer:
Liver function tests are crucial in monitoring a patient who has overdosed on acetaminophen, as they can indicate acute liver damage and guide treatment.
Step-by-step explanation:
The most important diagnostic study to monitor in a 15-year-old adolescent who was admitted to the hospital after taking an acetaminophen (Tylenol) overdose is b. Liver function tests. Overdose of acetaminophen can lead to acute liver damage, which is why monitoring liver enzymes such as alkaline phosphatase, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) becomes crucial. These enzymes typically rise dramatically in acute liver damage and are often measured in multiples of the Upper Limit of Normal (ULN). Elevated levels indicate liver distress and guide medical professionals in managing the overdose effectively.