answered May 20, 2010 at 04:35AM
Cancer does not necessarily show up in blood tests. Some cancers, like leukemia, may be diagnosed on a CBC, but in general a "normal" CBC cannot exclude cancer, while an abnormal test can't confirm it either. A CBC provides useful information about many diseases, but can't be used in isolation. Blood tests must always be interpreted in conjunction with all the patient's other clinical information.