There is no definitive reason that a CBC with DIFF with PLT blood test might be ordered. It is a diagnostic tool and can be used to follow the progress of a diagnosed illness. A DIFF is generally ordered when a CBC shows counts outside normal limits, according to Lab Tests Online.
The DIFF reveals the different types of white blood cells present, giving the health professional a indication of the condition of the immune system of their patient. This differentiates whether the patient suffers from an infection, an allergy, exposure to a toxin, or different medical situations involving white blood cells, such as leukemia and other types of cancers, states WebMD.
Platelet counts are ordered to examine potential clotting difficulties, including uncontrolled bleeding and the potential for a stroke caused by blood clotting, indicated by the patient having too many platelets. Information on platelet counts also indicates the possibility of hardening of the arteries, or atherosclerosis, states WebMD.
Results from WBC DIFF tests typically reveal the absolute counts of a variety of white blood cells, as well as showing their overall percentage of blood volume of the sample. This information, including types of white cells present, helps to identify the presence of infections as well as letting the medical professional treating the patient follow the reaction of the person to medicines being prescribed, states Lab Tests Online.