<P> A complete blood count (CBC) is a test panel requested by a doctor or other medical professional that gives information about the cells in a patient's blood . A scientist or lab technician performs the requested testing and provides the requesting medical professional with the results of the CBC . In the past, counting the cells in a patient's blood was performed manually, by viewing a slide prepared with a sample of the patient's blood under a microscope . Today, this process is generally automated by use of an automated analyzer, with only approximately 10 - 20% of samples now being examined manually . Abnormally high or low counts may indicate the presence of many forms of disease, and hence blood counts are amongst the most commonly performed blood tests in medicine, as they can provide an overview of a patient's general health status . </P> <P> In 1658 Dutch naturalist Jan Swammerdam was the first person to observe red blood cells under a microscope, and in 1695, microscopist Antoni van Leeuwenhoek, also Dutch, was the first to draw an illustration of "red corpuscles", as they were called . No further blood cells were discovered until 1842 when French physician Alfred Donné discovered platelets . The following year leukocytes were first observed by Gabriel Andral, a French professor of medicine, and William Addison, a British physician, simultaneously . Both men believed that both red and white cells were altered in disease . With these discoveries, hematology, a new field of medicine, was established . Even though agents for staining tissues and cells were available, almost no advances were made in knowledge about the morphology of blood cells until 1879, when Paul Ehrlich published his technique for staining blood films and his method for differential blood cell counting </P>

Ratio of wbc and rbc in human blood