The CA 27.29 blood test was approved for use in 1996 and is the only blood test that can be used to determine the presence of breast cancer. There are two other blood tests that are routine ordered, but these are to test for tumor markers and different types of cancer. The CA 27.29 blood test measures the amount of the antigen in the blood stream that is present only when there is active breast cancer.
As breast cancer progresses, so will the amount of the antigen that the CA 27.29 blood test is able to detect. By ordering this blood test in a series, the a doctor can determine if the cancer has metastasized or is responding to the treatment plan that has been developed.
The good news is that the CA 27.29 blood test can detect the presence of cancer. The bad news is that this test is not sensitive enough to determine if the cancers has spread to other organs. It helps to determine the likelihood of breast cancer spreading, but does not provide definitive results.
What Is a Normal Result?
For the CA 27.29 blood test, anything that is below 40 units per milliliter [U/ml] is considered to be a normal result. This means that women who have different test results that stay below 40 shouldn’t be concerned about the outcomes. A result that is 18 one day and then 26 on the next test both qualify as normal results.
It is also important to note that there are women who have high antigen levels above 40 U/ml that do not have anything condition at all. Although in studies it was only about 1% of women who had this result, it is still important to note because normal levels can vary based on the individual. This means discussing the results, even normal results, with a doctor is important.
When Is This Test Ordered?
If your doctor believes that you may have early stage breast cancer that has not been diagnosed or have breast cancer that may have spread, then the CA 27.29 blood test may be ordered to determine if there are cancer cells present. It is not generally used as a primary screening tool. To diagnose breast cancer, this test is usually used with imaging and other tests to determine the presence of a mass and the possibility of its malignancy.
Is This Blood Test Being Ordered Regularly?
Some doctors will order the CA 27.29 blood test on a regular basis, sometimes as often as every 3 months, in an effort to track if the cancer has metastasized. It is actually recommended that doctors don’t do this because the routine testing of markers hasn’t proven to be accurate. It is possible that a cancer will spread throughout the body and have the CA 27.29 blood test be lower than before, indicating a potential response to treatment.
The opposite is also true. The antigen levels may increase without any progression of the disease at all, creating a false positive. Sometimes a test result that is above 40 is considered proof that breast cancer has spread, but this isn’t always the case. The CA 27.29 blood test can create false positives for a number of different reasons.
- There may be breast disease present that is benign instead of malignant.
- There could be ovarian cysts affecting antigen levels.
- A woman may be in her first trimester of a pregnancy.
- Kidney disease or liver disease may also be present.
When there is a shortness of breath, unexpected weight loss, or headaches and muscle weakness present with increased antigen levels on the blood test, then a doctor may speak with your about treating a metastasized cancer. Without the symptoms, there may not be anything that can be treated or the wrong treatment may be recommended.
What Are the Chances of a False Positive?
Women who tested above 40 on the CA 27.29 blood test have a greater likelihood of a malignant condition than a benign condition. The highest rates outside of metastatic breast cancer were found with malignancies in the liver or in the ovaries. For the benign conditions that can cause a false positive, the most likely condition was cirrhosis, occurring in 1 in 4 women. Women who are lactating are 2x more likely to have a false positive on this test than women who have breast cancer that hasn’t been diagnosed.
If the results of your CA 27.29 blood test were positive, then schedule an appointment with your doctor immediately. You may need to have a change to your treatment plan.