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Blood Tests for Cancer

written by: R. Elizabeth C. Kitchen • edited by: Leigh A. Zaykoski • updated: 6/1/2011

This article discusses blood tests done for cancer. It talks about why they are done and how they are used in a cancer diagnosis. It also discusses what needs to be seen in them to indicate cancer.

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    What Are Blood Tests Done For Cancer?

    Blood tests, by themselves, will rarely indicate whether or not a person has cancer or not. If a doctor suspects that a patient has cancer they will often perform blood tests in order to get an idea about what it going on in the patients body. They may also order some blood tests in order to rule out certain other conditions.

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    Why Are Blood Tests For Cancer Performed?

    These tests may show cancer cells when examined under a microscope. A blood test that is commonly ran is called a CBC or complete blood count. This type of blood test measures how much there are of various types of cells in a patients blood. A doctor may see cancer cells, but they may also run this test in order to check for different diseases and conditions.

    These tests may also be performed to check for a various substances that may indicate cancer called tumor markers. These types of cells can be made by tumor cells, but they may also be made by normal cells in a patients body. A common tumor marker is called prostate-specific antigen or PSA. All men who still have their prostate gland will a detectable level of this tumor marker. If this specific tumor marker is highly elevated, then a doctor may to do further testing to check for prostate cancer.

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    How Accurate Are Blood Tests For Cancer?

    Blood tests for cancer must be performed and interpreted very carefully in order to be read correctly. Something as simple as a patients diet can affect the outcome of these types of blood tests. Other conditions can cause an abnormal blood test for cancer and many times those who actually have cancer will have normal blood test results.

    These tests are a good way to give the patients doctor clues as to what it going on with their bodies, but if cancer is suspected other tests will always be ran to conclude whether they have cancer or not. A biopsy is almost always required to confirm cancer and blood tests for cancer are typically used as a way to help monitor a patients help if cancer is diagnosed.

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    Mayo Clinic Staff. (2007). Cancer Blood Tests: Lab Tests Used in Cancer Diagnosis. Retrieved on February 16, 2009 from The Mayo Clinic. Website: