Asthma...my white blood count 18.4 (h)..do i need to take antibiotic to lower it or what can help ..thank u?

Depends....: if you are taking systemic steroids for your asthma, like prednisone, at the time this test was done, that could be the reason for the elevated white coun. This is a side-effect of steroid therapy. If you have other signs and symptoms of infection, like fever, change in color/consistency of sputum,etc., then you may need an antibiotic course. So, follow up with your doctor!