Can a blood test detect cancer in the body?

A doctor explains treatment to a patient.

When you go to the doctor for a routine checkup, they might ask to get some blood work done. These tests can reveal a lot about your health — like how well your organs are working or whether your body is responding to medication.

But can a blood test detect cancer? The answer isn't so simple. We’ll discuss common blood tests, how to interpret your results and what they can (and can't) tell you about cancer.

What can blood tests tell you?

Blood tests help doctors check for a variety of health conditions, from nutrient deficiencies to how well your organs are working. Your doctor may order one as part of a routine exam or to investigate certain symptoms. Some of the most common routine blood tests include:

• Complete blood count (CBC): This test measures red and white blood cells, platelets and hemoglobin (the main component of red blood cells). It's commonly used to check for infections, anemia and other blood-related conditions.
• Basic metabolic panel (BMP): Checks key substances in your blood, including glucose, chloride, globulin and potassium. This test provides insight into organ function, particularly the heart and liver.
• Comprehensive metabolic panel (CMP): Includes all the tests in a BMP, plus additional ones for albumin, alanine transaminase (ALT), ammonia levels and bilirubin. A CMP offers a more detailed look at liver and kidney function.
• Thyroid stimulating hormone (TSH) test: Evaluates how well your thyroid is working and can help diagnose conditions like hyperthyroidism and Graves' disease.

These tests offer valuable insights into different aspects of your health, but understanding what your results mean is just as important.

How do I read my blood test results?

Blood test results come with a reference range, which shows what's considered "normal" for that test.

But normal isn't the same for everyone.

These ranges are based on large groups of healthy people, but your results can be higher or lower for many reasons — age, sex, medical history, medications, even things like stress or dehydration. That's why a single test result doesn't always tell the full story.

Terms you may see in your test results include:

• Negative/normal: Nothing unusual was found.
• Positive/abnormal: Something was detected outside the expected range.
• Inconclusive/uncertain: The results weren't clear enough to say for sure. You may need another test.

If you've had blood work before, looking at trends over time can be more useful than just one result. Even small changes can signal something worth checking out. And if a result seems off, don't panic — medications, illness or even what you ate before the test can all affect your numbers. Your doctor can help you figure out what's worth paying attention to and whether follow-up testing is needed.

Can a blood test tell if I have cancer?

Your doctor may recommend blood tests if you're at risk for cancer or experiencing symptoms. These tests can provide important insights and sometimes detect signs of cancer. Some of the most common blood tests used in cancer screening include:

• Complete blood count (CBC) for cancer detection: While a CBC is often part of routine health screenings, in this case, doctors use it to look for abnormally high or low blood cell counts, which can be a sign of certain cancers, like leukemia.
• Tumor markers: These tests look for substances in the blood that may be linked to cancer. Tumor markers can be produced by cancerous cells or by the body in response to cancer. They can also help doctors monitor how well treatment is working.
• Circulating tumor cell test: This test checks for cancer cells that have broken away from a tumor and are circulating in the bloodstream. It's often used to monitor cancers like breast and prostate cancer.
• Blood protein test: Certain cancers, such as leukemia and lymphoma, can cause abnormal protein levels in the blood. This test helps detect those irregularities.

So, can a blood test detect cancer? Sometimes.

Blood work can help point doctors in the right direction, but it doesn't always provide a definite answer. If your doctor orders blood tests to check for cancer, it's important to remember that results alone don't confirm a diagnosis.

Even if your results are available through a patient portal, they don't always tell the whole story. If something looks concerning or unclear, don't try to interpret it on your own — talk to your doctor. They can explain what your results mean in the context of your overall health and whether further testing is needed.

Blood tests can feel overwhelming, but they can help catch potential health issues early. If you have questions about your results — big or small — your doctor is the best person to guide you through what they mean and what, if anything, needs to happen next.