Final answer:
Liver function tests are pivotal in assessing the severity of liver damage after an acetaminophen overdose, especially since ALT levels increase significantly in acute liver injury.
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 overdose is liver function tests (LFTs). Acetaminophen is known to cause liver damage when taken in high doses, and evaluating the liver's condition is crucial in this scenario. Liver function tests include various parameters such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, bilirubin levels, serum albumin, and total protein levels. These tests are specifically relevant because ALT levels rise dramatically in cases of acute liver damage, a potential consequence of acetaminophen toxicity.