Paediatricscommon
A 14-year-old girl is brought to the emergency department by her mother three hours after being found crying in her bedroom beside an empty packet of ibuprofen 200 mg tablets. She says she swallowed about ten and took nothing else, and denies drinking alcohol. She weighs 52 kg, is alert with normal observations, and her abdomen is soft. Her mother keeps amitriptyline, iron and paracetamol in the bathroom cupboard. Which one of the following blood tests is most likely to change her management?