The work of a Pathologists is to examine tissues and body organs from biopsies and also examine bodily fluids such as urine and blood and even pap smears to determine if a person has some sort of disease or other condition such as kidney disease, cancer etc.
So when you have your blood drawn as a routine check the blood sample is sent off to a pathologists who examines the blood to determine if you're healthy or something else is going wrong inside your body.