Blood tests for cancer diagnosis are usually non-conclusive. The fact is that there is no single reliable blood test to accurately diagnose cancer.

These tests, however, may help or guide the doctor in the diagnosis, but the doctor cannot stop his procedure of detecting and confirming cancer there. Cancer blood testing does, however, point to a direction of further specific tests. Blood tests, therefore, do have an important role to play in cancer detection.

However, in patients with this disease, early diagnosis and prompt treatment form the most important criteria to prevent the death of the patient and improve his survival rate.

On his way to confirming a cancer case, the doctor will use various diagnostic tools such as:

  • Imaging studies
  • specific blood tests
  • biopsies
  • genetic testing

In this article, we look at the routinely carried out blood tests that doctors use to detect cancer.

There are three commonly used blood tests for cancer

Complete blood count (CBC)

Complete Blood Count gives an idea of the count of the various blood cells.

Specifically, this cancer blood test measures the blood for

  • the count of red blood cells, which carry oxygen throughout the body
  • count of white blood cells, which fight infection, and
  • the number of platelets, which help with blood clotting

The test also measures hemoglobin, a protein present in the red blood cells that carries oxygen, and the hematocrit value, which indicates the ratio of red blood cells to plasma.

This test, besides giving other information will not be conclusive, except in cases of leukemia where a very high white blood cell count is seen. This will be an indication for a bone marrow biopsy.

Since certain cancer treatments may lower blood cell counts, doctors often carry out the CBC test to keep a watch on the cell numbers

Testing for blood proteins to detect cancer

This test, called protein electrophoresis, is performed to detect the levels of immunoglobulins (abnormal proteins of the immune system). The levels of immunoglobulins 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.

Tumor marker or cancer marker blood tests

Tumor markers are chemicals manufactured by malignant cells. They can be found in the blood, urine, and body tissues of the cancer patient.

Elevated levels of tumor markers give an indication of cancer. However, normal cells also produce tumor markers in certain nonmalignant conditions, like cirrhosis of the liver. This shows the limitations of this test in confirming the diagnosis of cancer.

These tumor marker blood tests for cancer serve the following purpose.

  1. These tests are used to screen a high-risk population to detect cancer.
  2. They can help to diagnose a specific type of cancer by identifying the specific tumor marker, which is typical of particular cancer.
  3. They also help to know the prognosis of cancer
  4. These tests 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 specific cancer. For example,

Test for cancer of the prostate

Doctors usually carry out the Prostate-Specific Antigen test (PSA) to detect cancer of the prostate.

PSA levels of 4.0 to 10.0 ng/mL may suggest a 25% possibility of prostate cancer. 10.0 ng/mL and above is dangerous and is suggestive of a 50% chance of having prostate cancer.

Elevated PSA levels are highly suggestive of prostate cancer, but high PSA levels can also be due to non-malignant conditions like benign prostatic hyperplasia (BPH), or a prostate infection. PSA levels also rise naturally, as you age. Elevated PSA levels, therefore, are not conclusive of prostate cancer.

Test for liver, testicular, and ovarian cancer

Alfafetoprotein test (AFP) is a tumor marker test in which high levels are indicative of cancers of the liver, testicles, and ovaries.

However, elevated AFP levels are also found in noncancerous liver diseases such as cirrhosis and hepatitis. High AFP levels, therefore, do not always mean cancer, and normal levels may be seen even when you have cancer.

Test to diagnose ovarian cancer

Cancer Antigen 125 test (CA125) measures the amount of the protein CA 125 (cancer antigen 125) in your blood. This test is used in the early diagnosis of ovarian cancer especially in women with a high risk.

High levels of CA125 can also be found in endometrial, peritoneal, and fallopian tube cancers. However, normal conditions, such as menstruation, and non-malignant uterine fibroids can also elevate CA125 levels.

Test for Thyroid cancer

The calcitonin test is primarily used to help in the diagnosis of C-cell hyperplasia and medullary thyroid cancer. It may also be used to evaluate the effect of treatment and to monitor the possibility of recurrence of thyroid cancer.

For example, higher levels of calcitonin could indicate that you have medullary thyroid cancer. In a post-treatment case, it could mean that your cancer has returned. Lower levels indicate that your tumor is shrinking.

Though specific for thyroid cancer, cancer of the breast, lung, or pancreas can also raise calcitonin levels.

Test for cancer of the testes and ovaries

Human Chorionic Gonadotropins (hCG) test is done to measure the amount of the hormone hCG in blood or urine. It is done to see if a woman is pregnant. This test may also be done to detect cancer of the ovaries or testicles.

However, false-positive tests can occur in a post-menopausal woman or if she is taking hormone supplements.

Any level above normal may indicate cancer. hCG levels can shoot up to 300-10,000 mIU/mL in some types of cancer. If your hCG or β-hCG levels are high while on anti-cancer treatment, your doctor may opt-in for a more aggressive line of treatment.

Cancerembryonic antigen test or CEA test for cancer

CEA is a protein that is found in blood and body fluids, most prominently, in colorectal cancer. The CEA test can also be useful for detecting malignancy of the pancreas, stomach, breast, and certain cancers of the thyroid and ovaries.

CEA is found raised in certain nonmalignant conditions also like cirrhosis of the liver, infections, heavy smokers, and benign tumors of the colon and rectum. CEA levels are also elevated in a growing fetus in the womb.

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 bladder.

Urine cytology is a test that looks for abnormal cells in your urine. It is used with other diagnostic tests to detect urinary tract cancers, usually of the urinary bladder.

Your doctor might recommend a urine cytology test if you have hematuria (blood in your urine) after he has ruled out other causes such as calculi and urinary tract infection.

Urine cytology is more useful to detect bigger and more aggressive cancers than slow-growing cancers.

To summarize:

You can, therefore, see that though cancer blood tests may indicate the presence of cancer, they may not be conclusive. Evidence that is more conclusive is required to start early cancer treatment because treatment in itself has severe side effects and is started only after all cancer tests have confirmed the diagnosis of cancer.