Blood tests are commonly used to assist health care providers in determining a cancer diagnosis. There are many different kinds of blood tests used for a cancer diagnosis. Most cancers will affect the levels of certain cells, hormones, and nutrients in the patient's blood. For example, if a blood test result shows that the patient's white blood cell count is lower or higher than normal, that is a big indication that something is wrong. There are many infections, diseases, and other medical conditions that can raise or lower these levels as well. This is why blood tests, while very productive, are very rarely used alone for a cancer diagnosis. In many cases, blood tests are performed during a patient's routine check up. However, if the blood tests show unusual or unhealthy results, the health care provider will most likely call for further testing. The additional testing will be chosen based on what levels are not normal, as well as the age, gender, and overall health of the patient.

There are multiple blood tests that can be used to diagnose cancer as well as many other diseases and/or infections.

Complete Blood Count:

The complete blood count consists of many different tests that evaluate the level of some of the most important cells. Cells such as white and red blood cells should always be at certain levels. If there are fewer or more white and/or red blood cells in a patient, that is a clear sign that the patient is not healthy. These levels can be altered by cancer, as well as many other diseases. The tests involved in the complete blood count include the white blood cell count, white blood cell differential, red blood cell count, red blood cell differential, hemoglobin, hematocrit, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and the red cell distribution width. All of these tests are equally important in assuring the patient's health.

Blood Protein Test:

Blood protein testing can also be very helpful in reaching a cancer diagnosis. Blood protein testing evaluates the levels of certain proteins in the patient's blood. Most types of cancer will either damage or completely destroy the patient's immune system. There are proteins in the body that help the immune system function properly. If cancer is present in the patient and it has damaged their immune system, the blood protein testing will show a lower level of these particular proteins.

Tumor Marker Test:
 
There are many different kinds of tumor markers. Tumor markers are substances that are produced by cancerous cells. These markers can be found in the patient's blood. Different tumor markers are examined for different kinds of cancer. A more commonly known tumor marker is CA 125 (cancer antigen 125), which is detected in cases of ovarian cancer, and AFP (alpha-fetoprotein), which is detected in cases of liver cancer. However, there is controversy over the use of tumor marker tests for a cancer diagnosis. Many health care providers suggest that this type kind of testing is not reliable, because many tumor markers can be made by healthy cells. Therefore, if a patients does not have cancer, there can still be tumor markers present in their blood and this will give both the patient and the health care provider a false positive test result. The debate over the use of tumor marker testing still continues.