What Causes Elevated White Blood Cell Count?

My husband just started having problems last week. 24 hours before systems started we both had a checkup with our primary care physician at her clinic. Started with fever around 103 degrees and stayed there now for about a week. Thought it was the flue. Bclinic.he is acting lethargic. Realized his blood pressure is to low now 100 over 66. Has been on blood pressure meds for about a year. He went to hospital yesterday. They tested many things. Chest x rays and cat scan and blood came back normal. But he had elevated white blood cell count and his ekg came back a little off. They sent him home with antibiotics and something for nusia. But now when he thinks he wants to walk he runs instead. He is also extreamly thirsty and drinking much more water than usually.