To investigate for cancer, the doctor may order blood tests that look for tumor markers, which are substances produced by cancer cells or tumors. These tests, like AFP and PSA, can become elevated in the presence of certain cancers.
Tumor marker tests are used to identify cancer but also to monitor the response of cancer treatment.
Although these tests can identify cancer, tumor markers can be present in the blood for benign reasons, like appendicitis, prostatitis, or prostate hyperplasia. Therefore, blood tests for cancer should be done alongside other diagnostic tests, like ultrasound or MRI.
The normal reference ranges will vary from lab to lab as well as from patient to patient, therefore it is important for these results to be interpreted by a health care professional.
Some blood tests for cancer that the doctor may order include:
What it tests: The alpha-fetoprotein (AFP) is a protein that is evaluated when looking at tumors in the stomach, intestines, ovaries or liver metastases.
Reference ranges: Generally, malignancy is suspected for values over 1000 ng/ml. Nonetheless, this value can also become elevated with cirrhosis or chronic hepatitis. These conditions can yield AFP values around 500 ng/ml.
What it tests: The mucin-like carcinoma-associated antigen (MCA) test is usually ordered to investigate breast cancer.
Reference ranges: In most cases, this test can identify cancer when results are over 11 U/ml. However, MCA levels can become elevated with other, less serious conditions, like benign tumors found in the ovaries, uterus or prostate.
Normally for breast cancer, the doctor will additionally order testing of CA 27.29 or CA 15.3 levels to monitor breast cancer evolvement and verify the response to treatment.
What it tests: The bladder tumor antigen (BTA) test is used to help detect bladder cancer and is usually ordered alongside the NMP22 test and the CEA test.
Reference ranges: Levels of BTA will usually be over 1 in the presence of bladder cancer. BTA can also be found in the urine, however, and can become elevated with less serious conditions, like kidney or urethral inflammation, especially in those who require catheterization.
What it tests: The prostate-specific antigen (PSA) is a protein that is normally produced by the prostate, but levels can be become significantly elevated in the presence of prostate cancer.
Reference ranges: When PSA levels in the blood are over 4.0 ng/ml, it may indicate the early development of cancer. Levels over 50 ng/ml may indicate the presence of metastases. To confirm a prostate cancer diagnosis, other tests should be done, such as a rectal exam and a prostate ultrasound, as levels can become elevated due to benign situations.
5. CA 125
What it tests: The cancer antigen 125 (CA 125) test is a marker that is used to both investigate for ovarian cancr and monitor its treatment. This test should be order alongside other tests to ensure an accurate diagnosis.
Reference ranges: Generally, ovarian cancer will produce CA 125 levels over 65 U/ml. However, levels can also become elevated with conditions like cirrhosis, cysts, endometriosis, hepatitis or pancreatitis.
What it tests: Calcitonin is a hormone produced by the thyroid that is produced by the thyroid and mainly becomes elevated in those with thyroid cancer. It can also become elevated with breast or lung cancer.
Reference ranges: Levels over 20 pg/ml usually indicate the presence of cancer, however abnormal results may also be a sign of pancreatitis, Paget’s disease and even pregnancy.
What it tests: Thyroglobulin levels are usually elevated with thyroid cancer, however this test should only be used for diagnosis when ordered with other tumor markers, like calcitonin and TSH. This is because thyroglobulin can become elevated even when thyroid cancer is not present.
Reference ranges: The normal range of thyroglobulin is between 1.4 and 78 g/ml. Anything above this is usually a sign of cancer.
What it tests: The carcinoembryonic antigen (CEA) can be used to test for different types of cancer. It is usually noted to be elevated with intestinal cancer, when the colon or rectum are affected.
Reference ranges: High CEA levels are indicative of cancer when levels are 5 times the normal value, which is up to 5 ng/mL in smokers and up to 3 ng/mL in non-smokers.
In addition to these tests, the doctor may also opt to test for other hormones or proteins, like CA 19.9, CA 72.4, LDH, cathepsin d, telomerase and HCG, which can yield abnormal results in the presence of cancer.
3. CA 15-3 marker
What it detects: The CA 15-3 marker is ordered to aid in the diagnosis of breast cancer. It helps identify the stage of the cancer, and can help with monitoring response to treatment.
Reference range: Results that are greater than 30 U/mL are suggestive of breast cancer. However, it is common for the CA 15-3 value to be altered in cases of lung, ovarian and colorectal cancer. Thus, the doctor normally recommends carrying out CA 15-3 to monitor the disease and not necessarily confirm the diagnosis.
4. CA 19-9 marker
What it detects: The CA 19-9 marker is mainly indicated to assist in the diagnosis of pancreatic cancer. However, this marker may also be useful in diagnosing colorectal, gallbladder or liver cancer.
Reference range: A CA 19-9 result is greater than 37 U/mL is indicative of malignancy. However, to confirm the diagnosis, it is recommended that other markers be measured as well.
11. Protein electrophoresis
What it detects: Protein electrophoresis is one of the main tests requested for the investigation and diagnosis of multiple myeloma, as it measures the amount of immunoglobulins in the blood. It also evaluates for the presence of abnormal immunoglobulins.
Reference range: High gamma globulin values, above 1.27 g/dL or greater than 18.8%, may be indicative of multiple myeloma, although the main reference value can range from lab to lab.
In addition to this test, a multiple myeloma diagnosis should be additionally confirmed with other laboratory tests, such as M-protein in urine, known as Bence-Jones protein, and blood tests, which normally show anemia, pancytopenia, increased calcium in the blood or kidney disease.
12. CD-20 marker
What it detects: The CD-20 marker is a tumor marker that is used to determine the treatment approach for non-Hodgkin lymphoma.
Reference range: This type of test provides a positive or negative result for the CD-20 protein, which is reported as CD20+ or CD20-. When the result is CD20+, treatment can be carried out using targeted therapy, with monoclonal antibodies, such as rituximab, for example.
13. c-Kit mutation test
What it detects: The c-Kit mutation test looks for changes in the C-kit gene. It is performed using a sample of blood, tumor tissue or myelogram, to diagnose gastrointestinal stromal tumor (GIST), acute myeloid leukemia (AML) or melanoma of mucosa. This type of test allows the doctor to determine the type of treatment that should be performed.
Reference range: The result of the c-Kit mutation test can be positive for mutations in the C-kit gene, or negative, when it does not present with mutations. Generally, other tests are needed to confirm the diagnosis of these types of cancer, such as CD34 or P-glycoprotein, for example.
Genetic testing for cancer
Genetic tests for cancer allow the diagnosis of the disease to be made more quickly and can help to guide the doctor in elaborating a more targeted treatment plan. Genetic tests help to identify abnormalities in the DNA of cells that may be related to or increase the risk for cancer. Some tests that may be ordered are a liquid biopsy, gene expression and whole-exome sequencing.
Is it possible to identify cancer with just a blood count?
Performing a routine blood count and other routine blood tests are not sufficient to identify cancer, however, depending on the abnormalities noted and symptoms presented by the person, the doctor may suspect a condition. Abnormal results may prompt further testing to investigate or rule out cancer.
How to confirm a cancer diagnosis
If cancer is suspected, the doctor will order tests to investigate for cancer or rule it out. They will often order diagnostic imaging tests alongside bloodwork, with examples including:
- Ultrasound: This test looks for lesions in organs like the liver, pancreas, spleen, kidneys, prostate, breasts, thyroid, uterus and ovaries.
- X-ray: This test uses radiation waves to look for changes to the lungs, spine and bones.
- MRI: This imaging tests detects changes in organs like the breasts, blood vessels, liver, pancreas, spleen and kidneys.
- CT: A CT scan is usually ordered if changes were noted in an X-ray. It is usually ordered to look further at lungs, liver, spleen, pancreas and joints.
In the majority of cases, a cancer diagnosis is confirmed through a combination of tests, like patent assessment, blood tests, MRI and biopsy. There are specific cancer symptoms that the doctor will evaluate and ask the patient about.