<P> Complete blood counts are done to monitor overall health, to screen for some diseases, to confirm a diagnosis of some medical conditions, to monitor a medical condition, and to monitor changes in the body caused by medical treatments . </P> <P> For patients who need blood transfusion, a blood count may be used to get data which would help plan an amount of treatment . In such cases, the person should have only one blood count for the day, and the transfusion of red blood cells or platelets should be planned based on that . Multiple blood draws and counts throughout the day are an excessive use of phlebotomy and can lead to unnecessary additional transfusions, and the extra unnecessary treatment would be outside of medical guidelines . </P> <P> A phlebotomist collects the sample through venipuncture, drawing the blood into a test tube containing an anticoagulant (EDTA, sometimes citrate) to stop it from clotting . The sample is then transported to a laboratory . Sometimes the sample is drawn off a finger prick using a Pasteur pipette for immediate processing by an automated counter . </P> <P> Before the advent of automated hematology anayzers, CBCs were performed manually, by counting cells in a diluted sample of blood on a device called a hemocytometer, and by viewing a slide prepared with a sample of the patient's blood (a blood film, or peripheral smear) under a microscope . However, manual blood cell counts are becoming less common, and instead this process is generally performed by the use of an automated analyzer . </P>

How does a full blood count machine work