Which initial tests should be performed for Madelyn's diagnosis?

The initial tests that should be performed for Madelyn's diagnosis are the acetaminophen level and toxicology screen. These tests are crucial when there is a suspicion of possible poisoning or overdose, particularly with acetaminophen, which is a common cause of toxicity in pediatric patients.

Determining the acetaminophen level helps assess the extent of exposure and guides further treatment decisions. A toxicology screen can also provide information about the presence of other substances that may have been ingested, allowing for a comprehensive evaluation of the patient's condition. Both tests are critical in identifying potential life-threatening situations early, allowing for prompt and appropriate medical intervention.

Other choices do not address the urgent need to assess for potential toxic exposure. Blood typing and crossmatch are relevant in cases of trauma or blood loss, while imaging studies like X-rays and MRIs are not first-line tests in acute poisonings. A urinalysis may provide useful information, but it would not be as pertinent as directly assessing for specific toxic substances.