Several workers inside a laboratory
22 December 2015

Can Cancer Be Detected In Blood Work?

Signs and symptoms are rarely enough to conclusively diagnose a patient with cancer. To confirm their suspicions, doctors turn to a wide range of diagnostic tests. Assisted by advanced technologies, physicians gather evidence and clues, looking for signs of rapidly-dividing cells.

Visual tests, like magnetic resonance imagining (MRI) and computed tomography (CT), can produce clear pictures of hidden tumors, growths that may or may not be cancerous. Blood tests can be another indicator, but only in certain circumstances.

Can Blood Tests Detect Cancer?  Several workers inside a laboratory

Sometimes, especially where blood cancers, like leukemia, lymphoma and myeloma are concerned. While most other cancers can’t be diagnosed definitively on blood work alone, doctors can still find evidence of a potential cancer’s presence in a patient’s blood.

 

Blood work can tell us a lot about how the body is functioning. By analyzing a patient’s blood under laboratory conditions, physicians can sometimes spot cancerous cells themselves, or chemicals that may be produced by cancer cells. Blood tests also give us clues as to how well other organs are working, which may be evidence that their functions are being impaired by cancerous growth.

After cancer is diagnosed, and a treatment plan has been decided on, doctors also use blood tests to monitor a patient’s response to therapy.

3 Ways Doctors Look At A Patient’s Blood

Doctors rely on numerous different types of blood test in diagnosing diseases. Each of these diagnostics gives physicians a new perspective on aspects of a patient’s health.

1. Complete Blood Count: Getting The Big Picture

To get a general overview of a patient’s health, many doctors order a complete blood count (CBC) first. After taking blood, physicians can analyze the number of red blood cells, white blood cells, platelets and hemoglobin in the sample to detect abnormalities. Many diseases, including cancers, alter these levels, changing the proportion of white blood cells to red blood cells, for example.

One major aspect of the CBC is called a “white cell differential.” White blood cells, or leukocytes, are part of your immune system. They take on most of the responsibility in responding to infectious diseases, but abnormalities in their levels can also be a sign of some blood cancers. White cell differential is also a helpful indicator in judging a patient’s response to chemotherapy.

2. Blood Smears: Taking A Closer Look

If the blood work results of a CBC turn up abnormalities, many doctors will order a blood smear next. Pathologists will take a single drop of blood and literally smear it across a glass slide. Using dyes, these experts can color the different types of blood cells and then interpret their relative concentrations.

The real point here, though, is to note specific changes to the appearance of cells, which may be cancerous themselves or herald the presence of a cancer.

3. Tumor Marker Tests: Mixed Results

Technically, tumor markers are chemicals produced by cancerous cells that end up floating around in a patient’s blood. Some tumor markers are also made by healthy cells in the presence of cancers. That sounds like a clear sign of malignancy, but it’s not. Lots of people without cancer have elevated levels of tumor markers and the use of these tests in cancer diagnosis is still controversial.

 

Doctors usually look for proteins that accompany cancer, but recently, physicians have also started analyzing abnormalities in DNA and gene expression as tumor markers, too, according to the National Cancer Institute.

There’s no tumor marker that all cancers produce as a rule, at least not one that’s been identified yet. But researchers have found proteins that specific types of tumor seem to produce:

  • Alpha-fetoprotein, a blood protein produced by amniotic fluid during normal fetal development, may be elevated in the presence of liver cancer and germ cell tumors like ovarian cancer and testicular cancer.
  • CA 19-9 is an antigen, a protein that may be manufactured by cancer cells and causes an immune system response. CA 19-9 levels are usually studied to manage pancreatic cancer, but a patient’s levels may also be elevated because of colorectal or esophegeal cancer.

Finding cancer markers in blood work isn’t enough to diagnose cancer, or screen patients for developing malignancies.

In most cases, the chemicals can be used to differentiate between malignant and benign conditions, but the tests aren’t specific enough for us to know that a cancer is producing the tumor marker. Their true value usually comes after a diagnosis, when variations in the level of a tumor marker can help us understand how well a treatment is working.

Follow Up: Diagnosing Blood Cancers

While blood tests are most useful in detecting cancers of the blood, the preliminary diagnostics we just covered usually aren’t sufficient to diagnose conditions like leukemia. Their results can be a warning sign, but to get the truth, doctors will turn to even more specific types of blood test, along with ones that look at bone marrow and lymph nodes.

Finding Changes In Genetic Information

Cytogenic tests provide evidence of changes to the genetic material in cells. Some types of leukemia can alter chromosomes, structures made up of protein and DNA in the nucleus of individual cells. Chromosomes are best seen when cells are dividing, so pathologists will take samples of a patient’s blood or bone marrow and then grow the cells in the lab. Philadelphia chromosome, a shortening of chromosome 22, is indicative of chronic myeloid leukemia.

Fluorescent in situ hybridization uses fluorescent dyes to light up specific chromosomes under a microscope. In this test, doctors are looking for BCR-ABL, a gene abnormality that ends up creating Philadelphia chromosome. Beyond chronic myeloid leukemia, BCR-ABL may be present in patients with lymphoblastic leukemia and acute myelogenous leukemia.


Blood tests become extremely important after a cancer diagnosis, when doctors are trying to decide on the best treatment method. Investigating a patient’s blood and bone marrow can help physicians know whether or not a therapy is working, by highlighting changes in chemical levels. Before a proper diagnosis, blood work is one piece in a much larger puzzle, and usually can’t lead to the truth on its own.

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