If you’re feeling worn out or have suddenly lost some weight, your doctor might send you for a blood test.

Blood tests are a common way health-care professionals detect, diagnose, and monitor a range of medical conditions.

But can they help us detect more serious conditions such as cancer? Let’s dive into the research.

How do blood tests work?

Blood tests are a technique used in the field of pathology, which is the study of the nature and causes of disease.

Blood tests assess what cells, proteins, and molecules are present in the blood. Health-care professionals use them to monitor things like organ health, nutrition levels, immune system function, and the presence of some infections.

To test for anaemia, for example, you would take a blood test and count the number of red blood cells in that blood sample. Another example is blood sugar testing, which is used to measure the glucose levels of a patient with diabetes.

What can blood tests tell us about cancer?

Currently, we can’t reliably diagnose most cancers using a blood test. One major reason is it’s often difficult to distinguish between cancer cells and normal, healthy cells. This is especially true when it comes to early-stage tumours.

But blood test results can give us clues about whether certain cancers are present in the body. So how do they do this?

1. By revealing abnormalities in your blood

Blood cancers will often cause clear changes in the number and types of cells in the bloodstream. We can measure these changes using a complete blood count, also known as a “full blood examination”.

This type of blood test counts all the different types of cells present in the blood: red blood cells, white blood cells, platelets, and more. Blood cancers arise when your body produces an abnormal amount of any type of blood cell. White blood cells, which fight infection, are the most common example. So a high number of one or more of these cell types may suggest the presence of a blood cancer.

But complete blood counts aren’t enough to make a conclusive diagnosis of blood cancer. We need to perform other tests to confirm whether the problem is a cancer or a different disease. These tests may include a biopsy or imaging techniques such as an MRI, CT scan, or X-ray.

2. By identifying “tumour markers”

We can also use blood tests to detect specific proteins which cancer cells often produce in greater numbers. These proteins are known as “tumour markers”.

One example of a tumour marker is prostate-specific antigen. This antigen is a protein made exclusively by the prostate gland. A healthy male will have only a small amount of prostate-specific antigen in his blood. In contrast, a male with prostate cancer will often produce abnormally high levels of this antigen. In this way, the prostate-specific antigen can serve as a “marker” of prostate cancer.

There are many different tumour markers used to identify different cancers. However, measuring tumour markers is not a foolproof solution. This is because they can be influenced by other factors. For example, an injury to or inflammation of the prostate gland could cause prostate-specific antigen levels to increase. So your doctor may perform additional tests to confirm if a person has cancer.

3. By locating rogue cells

For other types of cancer, blood tests can look for circulating tumour cells. Circulating tumour cells are produced when cancer cells break off from the original tumour and then enter the bloodstream. This usually only happens when a cancer reaches a more advanced stage and is metastatic, meaning it has spread to other parts of the body.

But this type of test is usually prognostic, rather than diagnostic. This means we can only use it to monitor the progression of a cancer which has already been diagnosed. So if a blood test does identify circulating tumour cells, it is best to conduct additional tests before proceeding with treatment.

So, are we close to creating a cancer-detecting blood test?

Unfortunately, we are yet to find a way to detect cancer with a single blood test. It’s a very difficult task, but researchers are making progress.

Circulating tumour DNA is a current topic of interest. These DNA molecules have mutations which distinguish them from healthy cells and can give information about the cancer they came from.

In one 2025 trial, Australian researchers measured the amount of circulating tumour DNA in 441 people with colon cancer to determine which patients would respond to chemotherapy. Another study from 2025 used circulating tumour DNA to monitor how 940 patients with lung cancer responded to different treatments.

One test did claim to successfully use circulating tumour DNA to detect more than 50 types of early-stage cancer. It’s known as the “Galleri test” and was first trialled in the UK in 2021. However, some experts have since raised concerns about the test’s effectiveness.

Researchers are also exploring other ways of using blood tests. In one 2025 study, Australian researchers adapted an existing test to use blood instead of tissue samples to identify known markers of ovarian cancer.

Another Australian study from 2025 investigated whether molecules other than proteins could serve as cancer markers. It found certain fats in blood can indicate if a patient with advanced prostate cancer will respond to treatment.

So, it looks like we’re still a while away from creating a cancer-detecting blood test. But with some time, effort, and robust research, it could be a possibility.

John (Eddie) La Marca, Senior Research Officer, Blood Cells and Blood Cancer, WEHI (Walter and Eliza Hall Institute of Medical Research) ; Cameron Lewis, Clinician Scientist, WEHI (Walter and Eliza Hall Institute of Medical Research) , and Sarah Diepstraten, Senior Research Officer, Blood Cells and Blood Cancer Division, WEHI (Walter and Eliza Hall Institute of Medical Research)

This article is republished from The Conversation under a Creative Commons license. Read the original article.