MSFinals-4809

A 30-year-old man is brought to the emergency department by his brother at 2 pm. He was found at home with 6 opened packets of paracetamol, an empty bottle of vodka, and an empty bottle of beer. His brother last saw him at 10 pm the night before. The patient admits to drinking the alcohol throughout the night and taking 3 packets of paracetamol at 2 am and the other 3 at 6 am. The estimated paracetamol ingestion is 18g. He denies using any other substances. Blood tests are ordered and he is immediately started on IV N-acetylcysteine. What is the most important prognostic factor for this patient?