A complete blood count with differential looks at each of the five white blood cell types and measures the percentage of each in the blood, explains MedlinePlus. The test also locates any immature or abnormal cells in the blood.
The five white blood cell types are neutrophils, monocytes, basophils, lymphocytes and eosinophils, claims MedlinePlus. Following the extraction of the blood, a special machine counts the number of each of the five cell types and then determines if the types are in the proper proportion compared to the others. If the blood types are out of proportion, or if there is an indication of abnormal cells, a disease may be present.
There is very little risk associated with a complete blood count with differential, according to MedlinePlus. However, since the arteries and veins in the body vary from one person to another and even from one side of the body to another, collecting a blood draw can be more difficult in some patients. Risks that occur due to having blood drawn include excessive bleeding, fainting or feeling dizzy. It is possible to have blood accumulate under the skin following this test, and there is a slight risk of infection any time the skin becomes broken.