Approach to the child with fever practice

A 3-year-old boy has had a fever above 39 degrees Celsius for six days despite regular paracetamol. Both eyes are red without any discharge or crusting. His lips are cracked and bright red and his tongue looks raw. A blotchy red rash that blanches under a glass covers his trunk. There is a tender 2 cm lump in the left side of his neck, and the backs of his hands and feet are puffy. He is miserable but alert, with no neck stiffness. Which one of the following laboratory findings would you expect?