My 6 Yr Old Grandson Has Had Intermittent Episodes Of

My 6 yr old grandson has had intermittent episodes of headache, low-grade fever and vomiting over past two weeks which has been passed off as a virus by his pediatrician, a clinic doctor and ER physicians. Last Thursday his white count was 22. Today he left pediatricians office and had a seizure, the first of his life, and at the ER his white count was 26. All tests including respiratory panels, strep, mono, ct scan and preliminary spinal tap results are negative or normal; however, tonight his white count is 31. He is currently on IV antibiotics and anti-seizure meds. He had 3 petit-mal seizures total. MRI with and w/o contrast results are pending. Is there anything other than leukemia or something life-threatening that this could be?