Blood tests may be the first step in diagnosing leukemia. However, additional testing is usually needed to make an accurate diagnosis.

Leukemia is cancer that starts in bone marrow stem cells. These are immature cells that otherwise would become white blood cells, red blood cells, or platelets.

Blood tests are an important tool in diagnosing leukemia. Although they can strongly suggest leukemia, your doctor will most likely order bone marrow tests to confirm the diagnosis and identify the leukemia type.

In some cases, your doctor might order bone marrow testing even though your blood tests didn’t indicate leukemia. That’s because in some types of leukemia, cancer cells stay in the bone marrow and don’t circulate in the blood.

Your oncologist, a doctor specializing in cancer, can also use blood tests to monitor the disease and see how well treatment is working.

If your first alert to leukemia comes from routine blood testing, you’re not alone. This happens because early symptoms of leukemia can be vague and easy to miss. It’s a good idea to speak with a doctor if you have unexplained:

Your doctor may recommend annual blood testing, but make sure to report any new symptoms that show up between visits.

These blood tests involve a simple blood draw from the arm. No fasting or other preparation is necessary. In general, it’s best to be well hydrated and not hungry. Your doctor will let you know in advance if there are any special instructions.

Getting blood drawn for these tests is a simple, routine procedure. The medical professional drawing the blood will place a tight band around your arm and look for the best vein.

After cleaning the skin, they’ll insert a small needle into your vein. Blood will flow into small vials, and they will remove the band. Then they will place a cotton ball or bandage on the injection site. It shouldn’t take more than a few minutes.

If blood tests make you feel sick or you have a fear of needles, make sure to let the physician giving the test know. They’ll be able to help you stay calm. The blood samples will go to a lab, so it may take several days before you get the results.

Leukemia affects the production of blood cells in the bone marrow, causing atypical white blood cells to crowd out healthy blood cells and platelets. If your doctor thinks you may have leukemia, there are several blood tests that can help assess what’s going on.

Complete blood count

A complete blood count (CBC) provides measurements of:

  • red blood cells (erythrocytes), which help move oxygen from the lungs to cells all around the body
  • white blood cells (leukocytes), which help defend against bacteria and viruses
  • platelets, which help the blood to clot, so you don’t lose too much blood if you get a cut
  • hemoglobin, a protein that helps red blood cells distribute oxygen
  • hematocrit, the amount of your blood that’s made up of red blood cells

White blood cell differential

A white blood cell differential is usually included with the CBC. For this test, the pathologist (a medical professional who studies diseases) smears a drop of blood on a slide. Then they examine it under a microscope.

This includes analysis of the overall appearance of blood cells and platelets, as well as measurements of the different types of white blood cells. These white blood cells are:

  • neutrophils, which defend against bacterial and fungal infections
  • eosinophils, which fight infections caused by parasites
  • basophils, which are part of the immune response against parasites and bacteria
  • monocytes, which remove foreign organisms and dying cells from the body
  • lymphocytes, which are B cells and T cells that make up your immune system

Many labs use automated differentials, which analyze the smear with a computer. If these detect an atypical result, they are then verified by a pathologist.

Flow cytometry

In this test, the blood sample is treated with special antibodies and passed through a laser beam. These antibodies attach to cells with corresponding antigens. When that happens, they give off light that can be analyzed by a computer.

This test helps confirm the presence of leukemia and identify the specific type.

Your blood counts can provide a lot of information about leukemia and your overall health.

When it comes to your CBC report, it’s important to remember that different labs use slightly different reference ranges or sometimes different units. Your result will appear next to the established typical range for healthy people.

Age, sex, and factors such as pregnancy can affect these ranges. For example, a recent study found that the total white blood cell count was elevated by 36 percent in pregnancy.

According to the Leukemia & Lymphoma Society, healthy people have results that fit into the following ranges:

Red cells: per microliter of bloodWhite cells: per microliter of bloodPlatelets: per microliter of bloodHematocrit: percent of blood composed of red cellsHemoglobin: grams per deciliter
Men4.7–6.1 million5,000–10,000150,000–400,00042–5214–18
Women4.2–5.4 million4,500–11,000150,000–400,00037–4712–16
Children4.0–5.5 million5,000–10,000150,000–400,00032–449.5–15.5

The white blood cell differential takes a closer look at your white blood cells and the percentage they make up in your blood. Typical ranges are:

  • Neutrophils: 55 to 70 percent
  • Lymphocytes: 20 to 40 percent, but may be higher in children under age 4
  • Monocytes: 2 to 8 percent
  • Eosinophils: 1 to 4 percent
  • Basophils: 0.5 to 1 percent
  • Band (young) neutrophil: 0 to 3 percent

You might see a flag when results are above or below the typical range. This does not mean you have leukemia. An atypical result may be due to another cause, such as an infection or immune disorder.

Some atypical characteristics point toward a particular type of leukemia.

For example, people with acute lymphocytic leukemia (ALL) usually have too many immature white blood cells called lymphoblasts, which aren’t typically found in the blood. They may also have a shortage of red blood cells or platelets.

Someone with chronic myelomonocytic leukemia (CMML) may be lacking some blood cells but have too many monocytes and a high total white blood cell count.

Your doctor will be able to fully explain your results and answer any questions you may have.

Blood tests are routine and safe, and any complications are usually mild. These can include:

  • multiple needle punctures if it’s hard to find a vein
  • brief lightheadedness
  • bruising or minor bleeding
  • swelling and pain
  • infection

When blood tests indicate any type of leukemia, additional bone marrow tests can confirm the diagnosis. Bone marrow and genetic tests can also determine the type of leukemia you have so that you can start treatment.

Treatment depends on the type of leukemia. The disease can be acute or chronic.

The 5-year survival rates for leukemia vary drastically based on the type and a variety of other factors. Your doctor will have the most accurate data for your situation and outlook.