Cancer Blood Test.
Blood testing for cancer cannot be a conclusive cancer test. It may help or guide the doctor in the diagnosis, but the doctor cannot stop his procedure of cancer detection there. Cancer blood testing does, however, point to a direction of further specific tests. Blood tests for cancer, therefore, do have their important role to play in cancer detection as explained below.
Cancer Blood Tests.
The previous post on how cancer is diagnosed tells of the various diagnostic investigations that are used to came to a conclusive diagnosis of cancer. Here we shall see what blood tests are used to detect cancer.
There are three commonly used blood tests for cancer.
- Complete Blood Count will give an idea of the count of the various blood cells. This test, besides giving other information will be not be conclusive, except in cases of leukemia where a very high cell count of WBCs will be noticed. This will be an indication for a bone marrow biopsy.
- Testing for blood proteins. This test, called protein electrophoresis, is performed to detect the levels of immunoglobulins (abnormal proteins of the immune system). The levels of immonoglobulins are elevated in certain cancers such as myeloma or multiple myelomas. If abnormal proteins are found, the doctor will order a bone marrow biopsy to confirm the diagnosis of myeloma.
- Blood Tests for Cancer or Tumor markers. Tumor markers are substances manufactured by malignant cells. It can be found in the blood, urine and body tissues. Elevated levels of tumor markers give an indication of cancer. However, tumor markers are also manufactured by normal cells in certain non malignant conditions, like cirrhosis of the liver. This shows the limitations of this test in diagnosing cancer.
This blood tests for cancer or tumor markers serve the following purpose.
(1) It is used to screen a high risk population as a blood test to detect cancer.
(2) It can help to diagnose a specific type of cancer by identifying the specific tumor marker which is typical of a particular cancer.
(3) This cancer test will help to know the prognosis of cancer
(4) This test will also allow the doctor to monitor the patient after treatment to look for a remission of cancer.
As mentioned above, a specific tumor marker test can indicate a specific cancer. For example,
- Prostrate Specific Antigen test (PSA) for cancer of the prostrate.
- Alfafetoprotein test (AFP) for liver cancer.
- Cancer Antigen 125 test (CA125) for ovarian cancer.
- Calcitonin test for thyroid cancer.
- Human Chorionic Gonadotropins test (HCG) for cancer of the testes and ovaries.
- Cancerembryonic antigen test or CEA test for cancer. CEA is a protein which is found in blood and body fluids, most prominently, in colorectal cancer. CEA test can also be useful for detecting malignancy of pancreas, stomach, breast and certain cancers of thyroid and ovaries. CEA is found raised in certain non malignant conditions also like cirrhosis of the liver, infections, in heavy smokers and in benign tumors of the colon and rectum. CEA levels are also high in a growing fetus in the womb.
It is seen, therefore, that though cancer blood tests may indicate presence of cancer, they may not be conclusive. More conclusive evidence is required to start cancer treatment, because treatment in itself has severe side effects and is started only after all cancer tests have confirmed diagnosis of cancer.
Urine Cytology for Cancer.
Microscopic examination of urine may reveal the presence of cancer cells in cancers of the urinary tract such as cancer of the kidneys, ureter and the bladder.
Further tests to conclusively arrive at a diagnosis of cancer are discussed in the next posts.
- Radiological Investigations to Detect Cancer.
- Cancer Biopsy.
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