White blood cells are a vital part of your blood and your body’s main defence against infection. Also called leukocytes, these specialised cells seek out and destroy bacteria, viruses, and other foreign invaders. Understanding what white blood cells do — and what happens when their numbers are too high or too low — can help you make sense of your bloodwork and have better conversations with your family doctor or walk-in clinic provider.
What Are White Blood Cells?
White blood cells are nucleated cells found in human blood. Unlike red blood cells, which carry oxygen, white blood cells have a nucleus and a lighter-coloured cytoplasm. They contain no haemoglobin, which is the protein that gives red blood cells their distinctive red colour.
White blood cells are also larger than red blood cells. They can measure up to 15 micrometres in diameter. However, they are far less numerous. For every white blood cell in your body, there are roughly 600 to 700 red blood cells.
In a healthy adult, a cubic millimetre of blood contains between 4,000 and 10,000 white blood cells. Your doctor may refer to this measurement as your white blood cell count, or WBC count, on a standard blood test.
The Five Main Types of White Blood Cells
Not all white blood cells are the same. There are five main types, and each plays a different role in keeping you healthy. Your doctor can look at the proportion of each type — called a differential count — to get a clearer picture of what is happening in your body.
Neutrophils
Neutrophils are the most common type of white blood cell. They are the first responders of your immune system. When bacteria or fungi enter your body, neutrophils rush to the site of infection and engulf the invaders in a process called phagocytosis. Neutrophils are a type of polynuclear cell, meaning their nucleus has multiple lobes.
Lymphocytes
Lymphocytes are the second most common type of white blood cell. They are central to your immune memory — the ability your body has to recognise and fight off germs it has seen before. There are two main kinds: B cells, which produce antibodies, and T cells, which directly attack infected or abnormal cells. Vaccines work largely by training your lymphocytes.
Monocytes
Monocytes are large white blood cells that act as a clean-up crew. They move into tissues and transform into cells called macrophages. These macrophages engulf dead cells, debris, and pathogens. Monocytes also help regulate inflammation in the body.
Eosinophils
Eosinophils are best known for their role in fighting parasitic infections. They also play a key part in allergic reactions. When eosinophil levels are high, doctors may investigate for allergies, asthma, or certain digestive conditions. Like neutrophils, eosinophils are polynuclear cells.
Basophils
Basophils are the rarest type of white blood cell. They release chemicals like histamine during allergic reactions and asthma attacks. Although they are few in number, basophils play an important role in the body’s inflammatory response. They are also polynuclear cells.
How White Blood Cells Are Produced
Your body produces white blood cells in the bone marrow. Bone marrow is the spongy tissue found inside your larger bones, such as your hip and thigh bones. The process of producing blood cells is called haematopoiesis.
Once produced, white blood cells travel through the bloodstream and into tissues throughout the body. Most white blood cells live for only a few days. However, some memory lymphocytes can survive for years, allowing your immune system to remember past infections.
Your body constantly adjusts the number of white blood cells it produces. For example, during an active infection, the bone marrow ramps up production quickly. This is why a high white blood cell count can signal that your body is fighting something off.
According to Health Canada, maintaining a healthy immune system involves a balanced diet, regular physical activity, adequate sleep, and avoiding smoking — all of which support healthy white blood cell function.
What Your White Blood Cell Count Means
A standard blood test called a complete blood count, or CBC, measures the number of white blood cells in your blood. This test is common in Canada and is often covered under provincial health plans. Your family doctor may order a CBC during a routine physical, or if you have symptoms like fatigue, fever, or frequent infections.
High White Blood Cell Count
A high white blood cell count is called leukocytosis. It often means your body is responding to an infection or inflammation. In most cases, it is a temporary and expected immune response. However, a persistently high count can sometimes point to more serious conditions, such as immune disorders or, in rare cases, blood cancers like leukaemia.
Other common causes of a high white blood cell count include stress, strenuous exercise, pregnancy, or certain medications. Therefore, a single elevated result does not automatically indicate a serious problem. Your doctor will consider your full health picture before drawing any conclusions.
Low White Blood Cell Count
A low white blood cell count is called leukopenia. It means your immune system may be weakened. This can make you more vulnerable to infections. Common causes include viral infections, autoimmune conditions, bone marrow disorders, or chemotherapy treatments.
Some medications can also lower white blood cell counts. In addition, certain nutritional deficiencies — such as low levels of vitamin B12 or folate — can affect production in the bone marrow. If your count is low, your doctor will likely order follow-up tests to find the cause.
For a thorough overview of how blood tests work and what your results mean, the Mayo Clinic’s guide to complete blood counts is an excellent resource.
Conditions That Affect White Blood Cells
Several health conditions directly affect how white blood cells behave or how many your body produces. Understanding these conditions can help you recognise warning signs early.
Infections
Bacterial infections typically cause a sharp rise in neutrophils. Viral infections, on the other hand, often cause a rise in lymphocytes. Your doctor can use the differential count — the breakdown of each type of white blood cell — to help determine whether an infection is bacterial or viral. This is important because bacterial infections may require antibiotics, while viral infections generally do not.
Autoimmune Conditions
In autoimmune diseases, the immune system mistakenly attacks the body’s own tissues. Conditions like lupus or rheumatoid arthritis can cause white blood cell counts to fluctuate. Furthermore, some autoimmune conditions can directly destroy white blood cells, leading to chronic leukopenia.
Leukaemia and Lymphoma
Leukaemia is a cancer that starts in blood-forming tissues, including the bone marrow. It causes the body to produce large numbers of abnormal white blood cells. These abnormal cells crowd out healthy blood cells. Lymphoma is a related cancer that affects the lymphatic system, which is closely tied to white blood cell function.
Early diagnosis greatly improves outcomes for these conditions. As a result, it is important not to ignore persistent symptoms or consistently abnormal bloodwork. The World Health Organization’s cancer fact sheet provides helpful context on blood-related cancers worldwide.
Allergies and Asthma
Elevated eosinophil and basophil levels are often associated with allergic conditions. If you have ongoing allergies, asthma, or eczema, your doctor may monitor these cell types closely. Managing allergies effectively can help keep these white blood cell levels in a healthy range.
When to See a Doctor
You should speak with your family doctor if you notice signs that your immune system may not be functioning well. These signs include frequent infections, wounds that are slow to heal, unexplained fatigue, swollen lymph nodes, or recurring fevers. These symptoms may prompt your doctor to order a CBC to check your white blood cell count.
If you do not have a family doctor, a walk-in clinic is a good option for getting a referral or initial bloodwork done. Most provincial health plans in Canada cover routine blood tests when ordered by a physician or nurse practitioner.
Remember, a single abnormal blood test result does not always mean something is seriously wrong. Your doctor will look at your full medical history, your symptoms, and may repeat the test before making any decisions. Always consult a qualified healthcare provider before drawing conclusions from your bloodwork or making changes to your health routine.
Frequently Asked Questions
What is a normal white blood cell count in adults?
A normal white blood cell count in healthy adults typically falls between 4,000 and 10,000 white blood cells per cubic millimetre of blood. This range can vary slightly depending on the laboratory your sample is sent to. Your doctor will interpret your result in the context of your overall health and symptoms.
What causes a high white blood cell count?
A high white blood cell count is most commonly caused by an active infection, inflammation, or your body’s response to physical or emotional stress. Certain medications, pregnancy, and intense exercise can also raise the count temporarily. In rare cases, a persistently high count may signal a blood disorder, so it is important to follow up with your doctor.
What does a low white blood cell count mean?
A low white blood cell count means your immune system may be less able to fight off infections. Common causes include viral illnesses, autoimmune conditions, chemotherapy, and certain nutritional deficiencies. Your doctor will likely run additional tests to determine the underlying cause and recommend appropriate next steps.
How can I naturally support healthy white blood cell production?
Eating a balanced diet rich in vitamins C, B12, and folate, getting regular sleep, exercising moderately, and avoiding smoking all support healthy white blood cell production. Staying up to date on vaccinations also helps your white blood cells maintain immune memory. Always speak with your doctor before taking supplements to support your immune system.
Are white blood cells the same as leukocytes?
Yes, white blood cells and leukocytes are the same thing — leukocyte is simply the medical or scientific term for white blood cell. Both terms refer to the nucleated blood cells that play a central role in your immune system. You may see either term used on your laboratory bloodwork results.
Is a white blood cell count test covered by provincial health plans in Canada?
In most Canadian provinces, a complete blood count — which includes the white blood cell count — is covered under provincial health insurance when ordered by a licensed healthcare provider. You can get this test ordered through your family doctor, nurse practitioner, or a walk-in clinic. Check with your provincial health authority for specific coverage details in your area.
Key Takeaways
White blood cells, also called leukocytes, are the frontline defenders of your immune system.
There are five main types: neutrophils, lymphocytes, monocytes, eosinophils, and basophils — each with a unique role.
A normal white blood cell count ranges from 4,000 to 10,000 per cubic millimetre of blood.
A high count (leukocytosis) often signals infection or inflammation; a low count (leukopenia) may indicate immune weakness.
White blood cells are measured through a complete blood count (CBC), which is widely available and typically covered by provincial health plans in Canada.
A healthy lifestyle — including good nutrition, regular exercise, and adequate sleep — supports healthy white blood cell production.
Always consult your family doctor or a walk-in clinic provider if you have concerns about your blood test results or immune health.
