A 5-Month-Old African American Boy Presents to the ER for Unexplained

A 5-month-old African American boy presents to the ER for unexplained fever and swelling of his hands and feet. The mother states that 2 days ago when she was putting on his socks she noticed that his socks no longer fit, and he was extremely fussy and crying when touching both his feet. She states that at the end of day both of his feet had increased in size and appeared swollen. Yesterday morning while breastfeeding she noticed that his fingers appeared swollen and describes them as being "sausage like" and that he felt feverish. She measured his temperature that morning and it was 101.5 F, (temporal) .
She denies any administration of medicine or antibiotics recently, or sick contacts. She states that their family just came back from a vacation in Colorado where they went skiing for the first time. Family history is negative except for a distant relative on the mother's side having a disease she describes "where his RBCs were shaped differently and would make him sick in colder weather". All newborn screening tests were negative.
You order a complete lab work-up and get back the CBC with differential results that show normocytic anemia, a low platelet count, target cells, and depranocytes also known as sickled cells. You suspect that your patient may have Sickle cell disease.
What test must you order is considered diagnostic for sickle cell disease?

A) Solubility test
B) Hemoglobin electrophoresis
C) Bone marrow biopsy
D) Flow cytometry