A 2 month-old febrile male is brought to your facility to be evaluated for loss of appetite, irritability, and an acute petechial rash. Rectal temperature is 102.8F. Which of the following diagnostic studies is the most important in this child’s evaluation?
A. white blood count and differentia
B. urinalysis
C. CSF analysis
D. serum glucose
E. chest X-ray (CXR)