Blood Tests Used to Diagnose Cancer

While no blood test can diagnose cancer, some blood tests can aid in the diagnosis of cancer. If cancer is suspected, blood tests may be ordered. There are also blood tests used to screen for cancer or monitor the return of cancer after treatment.

Complete Blood Count (CBC)

A complete blood count test (CBC) checks the levels of cells produced by bone marrow in the blood, such as

• Red blood cells
• White blood cells
• Platelets

CBC tests are performed during cancer diagnosis, particularly for leukemia and lymphoma, and throughout treatment to monitor results. 

CBC tests can also:

• Indicate whether cancer has spread to bone marrow.
• Detect potential kidney cancer through an elevated red blood cell count.
• Monitor the effects of chemotherapy

Chemotherapy treatment affects cell division in cancer cells and bone marrow cells, which can cause bone marrow suppression. A CBC test can monitor the following:

• Anemia due to low red blood cell levels
• Neutropenia from low levels of white blood cells increasing infection risk
• Thrombocytopenia when platelet levels are low

Comprehensive Metabolic Panel (CMP)

A comprehensive metabolic panel (CMP) provides your healthcare provider with information on your:

• Fluid balance
• Electrolyte levels
• Blood sugar
• Protein levels
• Liver functioning
• Kidney functioning

A CMP, performed with a singular blood draw, consists of 14 blood tests and can help assess your general health and diagnose and manage cancer.

A CMP can indicate certain types of cancer, depending on results. For example:

• High calcium (hypercalcemia) may be suggestive of lung, breast, esophageal, oral, kidney, ovarian, uterine, and cervical cancer, as well as lymphoma and multiple myeloma.
• Low blood glucose with hypercalcemia and raised liver enzyme may be a sign of liver cancer.
• High glucose levels can indicate pancreatic cancer.

A CMP test can also be used to monitor how cancer treatments affect your kidney or liver function and how calcium levels may affect your heart function and bones.

Tumor Blood Markers

When a tumor or cancer cell is in the body, substances released by them can be measured. These are called tumor blood markers and can monitor cancer progression, recurrence, diagnosis, screen, and stage cancer.

Tumor blood markers aren't typically able to diagnose cancer independently but can be combined with other tests for diagnosis. Tumor blood markers can also:

• Monitor the progression of cancer to see whether or not treatments are working
• Determine whether or not cancer has recurred after treatment or surgery
• Help determine the cancer stage
• Help determine the best treatment
• See if a tumor is growing or spreading (metastasized) to other parts of the body

Positive test results may be due to a noncancerous condition. Your doctor can help you understand the results of tumor blood markers and what they mean for you.

Genomic Testing

Genetic testing helps you and your healthcare provider understand how likely you are to develop cancer during your lifetime by checking for gene mutations. These gene mutations are specific inherited changes to a person's genes, which would be associated with the risk of developing cancer. Inherited gene mutations contribute to approximately 5 to 10% of all cancers.

While most genomic tests are performed on tissue biopsy, a few blood tests are used for this purpose. 

Genetic testing cannot tell you if you will develop cancer for certain but can reveal if you have a higher risk than the average population. If you have a family history that points to genetic causes of cancer or if these results might help with a diagnosis or treatment of cancer, your healthcare provider may recommend genetic testing.

While there are several options when it comes to genomic testing for cancers, these three below are the most common:

Electrophoresis

Serum protein electrophoresis tests antibodies in your blood to search for abnormalities that indicate myeloma cells are present. Myeloma cells produce a monoclonal antibody, meaning all the same. The discovery of this antibody in the blood helps to diagnose multiple myeloma. 

Circulating Tumor Cell (CTC) Test

A circulating tumor cell test (CTC) can check for blood biomarkers that show whether normal cells are transforming into cancer cells. CTC tests can help diagnose and screen patients who have a risk of developing cancer, such as a family history of the disease.

CTC tests are helpful in the early detection of cancer as well as monitoring treatment effectiveness over time. The only test currently approved for this purpose is called CellSearch CTC, which offers different prostate, colorectal, and breast cancer assays.

A Word From Verywell   

Ask your healthcare provider for help interpreting any results from blood tests. Further testing will likely be done before any diagnosis is made. Although cancer testing is stressful and frightening, it’s important not to jump to conclusions. Additional tests and discussions with your practitioner will help determine your diagnosis.