A previously healthy child presents to the emergency departm…

A previously healthy child presents to the emergency department (ED) with a 2 week history of fever, bruising and decrease activity. CBC with differential and a chemistry panel are drawn and the child is started on IV fluids. The nurse receives a call from the lab with some critical values – the WBC is 1.4(K), with 50% “blasts”, ANC is 200 and hemoglobin is 9.0%. Based on the presentation of the child above to the ED and the lab values, what test would be ordered to determine a definitive diagnosis for this child?