The CBC (Complete Blood Count, known as FBC/Full Blood Count in the UK) test is a test that measures the quantity of red blood cells, white blood cells, hemoglobin, usually platelets, the fraction of blood comprised of red blood cells (hematocrit), the mean corpuscular volume of the red blood cells, the mean corpuscular hemoglobin, and the mean corpuscular hemoglobin concentration. These tests are performed on the blood sample by a machine known as a hematology analyzer. The test can be performed in a few minutes, although some circumstances will cause the machine to call for a review by a human. Emergency tests are generally reported back within an hour, routine tests can take from 3-6 hours or longer if the sample must be sent to a central location for testing. The test results can be altered by many medications, by pregnancy, excercise, stress, smoking, and by mistreatment of the blood sample.

This test can be used to check for problems with fluid levels (such as those caused by dehydration and blood loss), abnormalities in blood cells, acute or chronic infections, allergies, clotting problems, congenital heart disease, cor pulmonale, pulmonary fibrosis, polycythemia vera, kidney disease, bone marrow failure, erythropoietin deficiency, hemolysis, leukemia, multiple myeloma, malnutrition, cytotoxins, autoimmune/collagen-vascular diseases, liver/spleen damage, radiation exposure, infectious or inflammatory diseases, stress, tissue damage, rheumatoid arthritis, malaria, sickle-cell anemia, and low oxygen tension. This versatility makes this test very useful to medical professionals.

Thanks to eliserh for the UK name info.