Blood Tests for Cancer Detection

In many cases, yes—but with caveats. Some blood tests can detect signs that suggest cancer may be present in the body, but they usually aren’t definitive on their own.^[3] Blood tests can identify abnormal levels of certain proteins, cell counts, or even fragments of tumor DNA, which may indicate the presence of cancer or prompt further diagnostic testing.^[4]

Importantly, not all cancers can be detected through blood tests, and a normal result does not always mean cancer is absent.^[3] Blood tests are typically used in conjunction with other diagnostic tools.^[2]

Your healthcare provider may recommend a number of blood tests to help detect cancer.

1. Complete Blood Count (CBC)

A CBC measures different components of your blood, including red blood cells, white blood cells, and platelets. Abnormal counts may be a sign of blood cancers like leukemia or lymphoma.^[5]

For example, a very high or low white blood cell count could indicate leukemia. Similarly, low red blood cell counts (anemia) or abnormal platelet levels can also be warning signs, though they may result from other conditions.^[5] While a CBC can signal a potential issue, it is not specific to cancer and usually prompts further investigation. Importantly, a CBC can flag blood cancers but cannot detect solid tumor cancers such as lung, breast, or colon cancer.^[3] CBCs are also used throughout cancer treatment to monitor how chemotherapy is affecting blood cell production.^[7]

2. Tumor Marker Tests

Tumor markers are substances—often proteins—produced by cancer cells or by the body in response to cancer. Common tumor marker tests include:^[6]

• Prostate-specific antigen (PSA): Elevated levels may indicate prostate cancer.
• CA-125: Associated with ovarian cancer.
• Carcinoembryonic antigen (CEA): Linked to colorectal and other cancers.
• Alpha-fetoprotein (AFP): May be elevated in liver or testicular cancers.
• CA 19-9: A protein marker associated with pancreatic cancer.

Tumor markers are often used to monitor treatment rather than diagnose cancer, as levels can also rise in non-cancerous conditions.^[6]

3. Blood Protein Testing

A blood protein test, also called protein electrophoresis, looks at the different proteins circulating in your blood, including those made by your immune system. Cancers that affect antibody-producing cells—such as multiple myeloma—can cause an abnormal spike in certain proteins that this test can detect.^[2]

4. Circulating Tumor DNA (ctDNA)

One type of liquid biopsy looks for circulating tumor DNA (ctDNA)—fragments of DNA shed by tumors into the bloodstream. These tests are less invasive than tissue biopsies and can offer valuable insights into genetic mutations present in the cancer.^[7]

This approach is particularly promising for tracking changes in tumors over time and identifying targeted treatment options. However, it may not detect all cancers, especially those that do not shed much DNA into the bloodstream.^[7]

5. Circulating Tumor Cells (CTC)

A related but distinct type of liquid biopsy looks for circulating tumor cells (CTCs)—whole cancer cells that have broken away from a tumor and entered the bloodstream, rather than DNA fragments. The FDA has cleared a CTC test for use in metastatic breast, colorectal, and prostate cancers, with a count of 5 or more CTCs per 7.5 mL of blood considered a clinically significant threshold.^[10]

Like ctDNA testing, CTC tests are typically used to monitor existing cancer rather than screen for new disease in people without a diagnosis.^[10]

6. Multi-Cancer Early Detection (MCED) Tests

MCED tests, like the Galleri® test, detect signals from multiple types of cancer with a single blood draw. These tests analyze methylation patterns in DNA to identify the potential tissue of origin.^[8]

Early research has shown promise, but MCED tests are still new and not yet a standard part of screening protocols.^[8] They should be used in consultation with a healthcare provider.

Blood tests can detect a range of cancer-related indicators:^[3]

• Abnormal cell counts (CBC)
• Elevated protein levels (tumor markers)
• DNA mutations and tumor signals (liquid biopsy, MCED)
• Inflammation or immune response

These results often lead to additional testing like imaging (MRI, CT scans) or a biopsy to confirm a diagnosis.^[2]

Blood tests can also help track how cancer is responding to treatment over time. For instance, falling levels of a tumor marker like PSA or CA-125 during therapy can indicate that the cancer is shrinking or responding well. In contrast, rising levels may suggest the need to adjust treatment or conduct further evaluations.

Routine blood work, such as a standard CBC or metabolic panel, may sometimes reveal abnormalities that prompt further investigation.^[5] However, these tests are not designed specifically to detect cancer and may miss early-stage or asymptomatic cancers.^[2]

In general, healthcare providers rely on a combination of medical history, physical exams, lab work, and imaging to build a complete picture of your health. Routine tests are best viewed as an early alert system—not a final diagnosis.

Blood tests are powerful tools, but they are not foolproof. Here are a few limitations:^[2,6]

• False positives: Non-cancerous conditions (like infections or benign tumors) can cause abnormal results.
• False negatives: Some cancers don’t produce detectable markers, especially in early stages.
• Limited scope: Most blood tests are best used in combination with other diagnostic methods.

That’s why blood tests are often considered one piece of a larger diagnostic puzzle rather than a standalone solution.^[2]

Researchers are continuing to improve the sensitivity and specificity of these tests. Advances in genomic testing, machine learning, and biomarker discovery may expand the range of cancers detectable through blood and reduce the rate of false results.

You may consider getting a blood test if you:^[2]

• Have a family history of cancer
• Are experiencing unexplained symptoms (fatigue, weight loss, persistent pain)
• Are age 50 or older
• Want to supplement routine screenings like colonoscopy or mammograms

Talk to a healthcare provider about your risk factors and whether a blood-based cancer screening is appropriate for you.^[3]

People at higher risk—such as those with BRCA mutations or smoking history—may benefit from earlier or more frequent screening. Personalized plans may combine blood tests, imaging, and genetic risk assessment for a comprehensive approach.

At Everlywell, we offer convenient at-home lab tests that help you take charge of your health. While not diagnostic for cancer, our 360 Full Body Test provides a comprehensive view of key health markers—an excellent tool for those wanting to monitor well-being and catch issues early.^[9]

Take a proactive step. Explore our 360 Full Body Test to better understand your health today.