Would blood counts be low if a person has cancer?

It depends.: First, understand that there are many causes of a low blood count besides cancer, as well as different "types" of "low blood counts." Second, it depends on the type of cancer. For example in some lymphatic or bone marrow cancers, the white blood count can be high initially and the red blood cell count low. Conversely, many treatments for cancer can lower both red and white blood cell counts.