A 5-year-old male presents to the clinic for evaluation of a rash of new onset. His mother first noticed it three days ago, and complains that the affected area has continued to increase in size. On...

A 5-year-old male presents to the clinic for evaluation of a rash of new onset. His mother first noticed it three days ago, and complains that the affected area has continued to increase in size. On examination you notice multiple pinpoint hemorrhages on his skin. Similar findings are visible on his gums. You also note the presence of blood in his right nares. His mother denies recent illness, and reports no family history of bleeding disorders. Would you order a PTT, PT, bone marrow biopsy, or bleeding time, and why?