A complete blood count (CBC) is one of several blood tests commonly performed on people who have leukemia or who are suspected of having the condition. A CBC measures the number of each of the main types of blood cells: platelets (thrombocytes), red blood cells (erythrocytes), and white blood cells (leukocytes). While leukemia typically leads to a high white blood cell count (WBC), the condition and some of its treatments can sometimes lead to low white blood cell counts.

The Role of White Blood Cells

White blood cells are manufactured by the bone marrow, the spongy tissue found in the center of some of the larger bones in your body. Under normal conditions, a person’s bone marrow produces plenty of stem cells that develop into the various WBCs. There are five primary types of white blood cells:

• Basophils
• Eosinophils
• Lymphocytes
• Monocytes
• Neutrophils

Each type plays a specific role, responding to different types of foreign bodies in specific ways. In general, normal WBCs fight off bodily infection from invading bacteria, viruses, and other pathogens (infection-causing organisms). WBCs are the soldiers of the body’s immune system.

Normal White Blood Cell Counts

The normal range of white blood cells found in every microliter of blood differs for adults and children. According to the Leukemia & Lymphoma Society, normal blood cell count falls within the following ranges:

• 5,000 to 10,000 WBCs per microliter of blood for men
• 4,500 to 11,000 WBCs per microliter of blood for women
• 5,000 to 10,000 WBCs per microliter of blood for children

Different types of WBCs are counted by a measure called white blood cell differential. The differential is the ratio of the various WBC types. In a normal blood count, the WBC differential comprises numbers within the following ranges:

• 55 percent to 70 percent neutrophils
• 20 percent to 40 percent lymphocytes
• 2 percent to 8 percent monocytes

Basophils and eosinophils comprise the rest of the blood.

How Does Leukemia Affect White Blood Cells?

When a person has leukemia, their body produces an excessive amount of abnormal white blood cells. These leukemia cells don’t function properly. They’re not able to fight infection from viruses and bacteria, like their normal counterparts, leaving a person’s immune system vulnerable to attack. The overproduction of these dysfunctional WBCs crowds out other cells in the bone marrow and interferes with how bone marrow produces red blood cells and platelets. Leukemia and cancer treatments often have an impact on blood counts in general, including red blood cells and hemoglobin, and on platelets.

High vs. Low White Blood Cell Counts in Leukemia

It’s important for doctors to track WBC counts in a person living with leukemia or undergoing treatment for leukemia. A low WBC or a high WBC count can provide important information for a doctor, helping them to interpret symptoms and achieve good treatment outcomes.

Low White Blood Cell Count

A low WBC count, also called leukopenia, could indicate that a person undergoing leukemia treatment has an infection, resulting from the low count. It can also indicate a person is not getting proper nutrition, including specific vitamins or iron.

Both leukemia and some therapies to treat it (such as chemotherapy) can tax the immune system and cause low WBCs. Chemotherapy is very effective at killing fast-growing cells. Unfortunately, chemotherapy doesn't differentiate between good cells, like neutrophils, and bad cells, like leukemia cells. That’s why low WBCs are common during cancer treatment. A person’s blood cell count usually returns to normal on its own once treatment is over.

High White Blood Cell Count

A high white blood cell count may indicate that the body is fighting an infection. It is also an indicator of leukemia. High WBC counts are also a common side effect of certain medications used in leukemia treatments, including chemotherapy and radiation therapy. WBC counts can temporarily increase after recovery from treatment. CBCs are commonly used as an indicator to adjust a person’s treatment regimens.

Other Conditions That May Cause Low WBC Counts

Having a low or high WBC is not always an indication of leukemia. Five percent of people will experience a high or low WBC in their lifetime. In fact, several noncancerous conditions can lead to an abnormal WBC count. For example, autoimmune diseases like rheumatoid arthritis (RA), which can cause high WBCs, and excessive alcohol use can lead to a low WBC count. Certain racial and ethnic groups may naturally have a lower number of circulating WBCs.

How To Avoid Infections

A person with leukemia is susceptible to foreign pathogens (viruses, bacteria, and allergens) and less equipped to fight off and heal from infections. This is especially true for a person undergoing chemotherapy as part of their treatment. Having a low white blood cell count means that some infections may become life-threatening, so it’s important to take steps to help cut down your risk of getting sick when your immune system isn’t in its strongest fighting form.

Avoid Situations That May Put You at Risk

You can pick up a bacterial infection (such as pneumonia or an ear infection) from the air, water, soil, or food. You can catch a viral infection (like a cold, flu, or COVID-19) from being around another person with the infection. Remain aware of your surroundings, the activities you get involved in, and the number of people you interact with. When you’re at increased risk of infection, it’s best to avoid scenarios that are high-risk.

If you do get sick, or even suspect you’re not well, promptly addressing the illness is vital. If you think you may have an infection, reach out to a health care provider on your leukemia treatment team immediately.

Wash Your Hands

Keeping your hands clean is another effective way to help avoid catching a secondary infection. Wash your hands thoroughly and often, ideally with an antibacterial soap and hot water, especially after you use the restroom, after you have been in a public space, and before you eat or prepare food. You can also use antiseptic hand sanitizer when you’re away from a sink or bathroom.

Learn About Your Diagnosis and Treatment Side Effects

Understanding your diagnosis and how it affects your immune system may help you avoid secondary infections. Your risk may vary depending on your leukemia’s progression and treatment phase. Knowing the risks to your health can better inform your choices and the levels of risk you feel comfortable taking. It’s also important to know the symptoms of a possible infection, such as fever, so that you can contact your health care provider at the first sign of illness.

Lower Stress Levels

Being under a great deal of stress can take a toll on the immune system. Learning of a cancer diagnosis, undergoing leukemia treatment, and making necessary life adjustments can be stressful. Consider calling on your support system, seeing a therapist, or trying mindfulness and meditation to help reduce your stress where possible.

Connect With Others Who Understand

If you have leukemia, it can help to have the support of others who understand. MyLeukemiaTeam is the social network for people with leukemia and their loved ones. More than 9,000 members come together to ask questions, give advice, and share their experiences with others who understand life with leukemia.

Do you have tips for managing low white blood cell counts? Share your thoughts in the comments below, or start a conversation by posting on MyLeukemiaTeam.