Can Blood Tests Detect Cancer?

blood tests
Blood tests alone cannot detect cancer but can help guide a cancer diagnosis

In most cases, blood tests alone cannot detect cancer. With the exception of blood cancers, blood tests cannot distinguish between cancer or other noncancerous conditions. But the test results can help your doctor understand what is going on inside your body and whether an infection or inflammation in your organs signals something serious.

Complete blood count (CBC)

CBCs evaluate the number and shape of the blood cells in your body. These include red blood cells (RBCs), white blood cells (WBCs) and platelets. Blood cancer may be suspected when the WBC count is very high, or abnormal forms of these cells are found in the blood.


This is a type of blood protein test that can be used in the diagnosis of multiple myeloma, which is cancer of the bone marrow, a spongy tissue found in the bone center. Results are represented in a graphical form, and spikes in particular proteins may indicate that multiple myeloma is present.

Tumor marker tests

Tumor markers are substances produced by cancerous cells and are elevated in certain types of cancer. However, since normal cells can also produce tumor markers in many noncancerous conditions, tumor marker tests are not used to confirm a cancer diagnosis. Instead, they are mainly used to track your response to cancer therapy and to determine whether the cancer is growing. Your doctor will schedule follow-ups and monitor your levels over several months.

Chart: Examples of tumor markers against associated cancers
Tumor marker Associated cancer
PSA (prostate-specific antigen) Prostate cancer
CA 125 Ovarian cancer
AFP (alpha-fetoprotein) Liver cancer

HCG (human chorionic gonadotropin)

Testicular cancer and ovarian cancer
Calcitonin Medullary thyroid cancer
CA 19-9 Pancreatic cancer, esophageal cancer and gallbladder cancer

What Other Tests Are Used to Diagnose Cancer?

Once your doctor evaluates your blood test results, they will order other tests as necessary to make a diagnosis. These tests may include:

  • Ultrasound: Involves moving a probe on a specific area such as the abdomen and using sound waves to capture images of the organs.
  • Computed tomography (CT) scan: Uses multiple X-rays (radiation) to provide detailed images of the organs. Sometimes, a CT scan is combined with a positron emission tomography (PET) scan to determine how much the cancer has spread locally or distantly.
  • Magnetic resonance imaging (MRI): Provides detailed pictures of the organs, but unlike a CT scan, it uses magnetic waves.
  • Biopsy: A surgical procedure that takes a sample of suspicious cells for testing. A biopsy is usually necessary to make a definitive diagnosis. For example, after your CBC tests point toward blood cancer, your doctor will order a biopsy of the bone marrow to confirm the diagnosis.

After evaluating your test results and making a diagnosis, your doctor will then stage the cancer to find the right treatment plan for you. They will discuss the benefits and risks of each cancer therapy based on your age, overall health and preferences.

Cancer blood tests: Lab tests used in cancer diagnosis.