Traditionally performed in physician offices and laboratories, blood tests are useful tools for uncovering disorders in the human body. They detect abnormally high or low levels of substances that may indicate a variety of diseases, including cancer.

Blood tests may be ordered during diagnosis to rule out other diseases and disorders. Although they are used to help detect cancer, additional tests are usually necessary to verify the diagnosis. They may also be used to determine a person’s risk of developing cancer, or to screen for cancer before signs and symptoms develop.

In people with cancer, blood tests may be used to monitor the progression of the disease, and the effectiveness of treatment. They may also be helpful in detecting recurrent cancer (cancer that has returned after treatment). In many medical facilities, blood is drawn by a phlebotomist, who is a medical laboratory assistant specially trained in collecting and handling blood.

Depending on the amount of blood required for the test, blood can be drawn from a vein puncture (venipuncture), artery puncture (arterial puncture) or skin puncture. Obtaining a blood sample only takes a few minutes and most patients find them to be almost painless. Some blood tests may require fasting or other preparation. However, for most blood tests, there is very little preparation beforehand, and people can generally return to their usual daily activities following testing.