On blood work I want to know what is CBC w Dif w Pit Mean, what does this test for? Thks

I  am a 73 year old woman with sickle cell traits. I get my annual check up yearly. I feel well on only one medication for high blood pressure(triamth/hctz 37.5 mg) I don't think there is anything wrong with me, only this year the doctor tells me to take more blood work and I refused because I have no known symptoms. I was told by my Dr. that there is a little blood in the nuclear and my hemoglobin normal.