The complete blood count is an important follow-up and screening tool we have all used more than once. It is one of the first exams doctors ask when there’s an infection or any other alteration. The complete blood count includes the white blood count, which is an estimate of how many white blood cells there are in your blood.
The white blood count is very important because these cells have a key role in defending your body against infection. White blood cell creation and release in the blood are triggered and stimulated during infection. A functioning immune system will respond against disease by increasing the total count of white blood cells. Thus, it is a helpful measure to see how is your immune system reacting, and what type of disease your body is trying to counter.
In this type of test, a sample of your blood will be taken, and you don’t need any special preparation to evaluate your white blood cell count. Thus, you can use this exam in emergency settings, and it won’t be altered according to your eating patterns or any fasting state.
In this article, we will go through white blood cell count in detail and give you an insight of what to expect in cases of normal white blood cell count, and how to interpret abnormal results.
Normal white blood cell count
To understand white blood cell count, it is important to know what it measures. There are 5 main types of white blood cells. They are:
- Basophils: It is less abundant compared to other white blood cells, and they are typically responsible for allergic reactions. The normal proportion of basophils is 0.5% of the total number of white blood cells.
- Eosinophils: They are mainly phagocytic cells, which means they are attracted and swallow microorganisms to destroy them. These cells are usually found as 1 to 3% of the total number of white blood cells.
- Lymphocytes: There are many types of lymphocytes, but all of them look the same under the microscope and are counted as a total lymphocyte count. They are very abundant in the blood, representing up to 30% of the total number of white blood cells.
- Monocytes: They are also known as macrophages when they migrate to the tissues, but in the blood, they are called monocytes. These represent up to 8% of the total number of white blood cells.
- Neutrophils: By far the most common white blood cells, and the first line of defense against disease. Neutrophils destroy bacteria and fungi with a series of enzymes and turn into pus when they die in battle. In normal settings, they represent 60 to 70% of the total white blood count.
The normal white blood cell count is 4,500 to 11,000/μL, but the normal value range may vary from one laboratory to another.
High white blood cell count
A high blood cell count is also known as leukocytosis, and it is typically diagnosed when levels are higher than 11,000/μL. The white blood cells are produced by the bone marrow when the immune system is stimulated in some way. They are cleared from the blood by the spleen, and these cells are very important for inflammation. Thus, a high blood cell count usually points to one of the following causes:
- Infections: A common cause of high white blood cell count, usually a bacterial infection.
- Leukemia and lymphoma: They are cancers related to the immune system, and activate the production of new white blood cells by genetic aberrations and through the activation of oncogenes.
- Extensive tissue damage: In trauma, extensive wounds or burns, the immune system becomes activated, and white blood cells are typically found in higher levels.
- Acute or chronic inflammation: In autoimmune disease, allergies, and other inflammatory problems, white blood cells are usually higher than normal or borderline.
- Cigarette smoking and drugs: Cigarette smoking triggers inflammation and stimulates the production of white blood cells. Similarly, patients who are using corticosteroids heparin, lithium, albuterol, and similar drugs, are likely to find a higher level of white blood cells in their complete blood count.
Cases of high white blood cell count are usually investigated by considering the proportion of white blood cells. This will give a very important clue in cases of infectious diseases. When there’s a higher proportion of neutrophils, bacterial infections are the likely cause. In cases of high levels of lymphocytes, the viral disease is commonly suspected. Higher eosinophil count typically points out to fungi or parasitic infections, and a higher count of basophils is associated with inflammation and allergies.
Low white blood cell count
A low white blood cell count is also known as leucopenia and typically found below 4,500/μL. White blood cells are produced in the bone marrow, and the proportion may become affected in autoimmune disease. They are eliminated in the spleen, and some environmental factors may also impair their production.
The most common causes of low white blood cell count are as follows:
- Bone marrow problems: Tumors or disease in the bone marrow may cause an alteration in the number of blood cells it produces.
- Certain drugs: Especially chemotherapy for cancer, but other drugs may also be involved. Some antibiotics and diuretics may cause a depletion of the bone marrow. Other drugs include anti-thyroid hormone drugs, captopril, medications to control seizures, and more.
- Liver and spleen problems: They cause a lower white blood cell count as the cells to become trapped and eliminated in the structure of the diseased spleen and liver.
- Radiation therapy: Typically used against cancer, it is a common cause of bone marrow depletion and low white blood cell count.
- Leukemia and other cancers: Cancers that affect the bone marrow directly or indirectly cause depletion of the stem cells and may result in low white blood cell count.
- Physical or emotional stress: An increase of cortisol during acute stress causes a depletion of the immune system and transient reduction of the white blood cell count.
How blood cancers affect blood counts?
You may have noticed that blood cancers and leukemia can cause both a high or low white blood cell count, and you may ask how is this possible. It has to do with the natural history of the disease.
Leukemia is an alteration of the stem cells in the bone marrow. At the beginning of the disease, white blood cell counts are extremely high, much higher than we can find in common cases of infections. But such high levels do not mean your body is protected against infection, because they are non-functioning and immature cells that do not defend your body correctly. Thus, there’s a high risk of infection and an elevated white blood cell count.
But at some point, leukemia cells become stuck or infiltrated in the bone marrow. When they do, they cause severe alterations in the normal functioning of the stem cells in the bone marrow, and we will see a depletion of one or more types of blood cells. That’s why we see anemia in a late phase of leukemia, because the bone marrow is affected, and red blood cell production becomes impaired. We can also have a low count of white blood cells and platelets with associated health problems.
Should you keep track of your white blood counts?
Lymphocytes and neutrophils are the most important white blood cells in your blood count, and they only have a circulating half-life of a few hours or a few days. Thus, white blood counts are variable in time, and only reflect the state of infectious diseases and the stage of leukemia in particular cases that should be analyzed by a doctor.
Keeping track of white blood counts is appropriate to follow-up patients in cases of severe infection, and to make important decisions in patients with leukemia. For example, taking a new blood sample after antibiotic therapy will help us understand how the antibiotic is dealing with the infection. And in cases of leukemia, a follow-up of white blood count is essential to know whether or not the disease is being controlled with chemotherapy and other therapeutic options at hand.
Thus, if you had a normal white blood cell count, there is no reason to keep track of your numbers for a while, unless you start displaying new signs and symptoms. Conversely, if you had an alteration in your white blood count, trust your doctor and follow his recommendations. Ask him when is it appropriate to have a follow-up and do not try to interpret the results of your tests by yourself.
References
Hutchison, R. E., McPherson, R. A., & Schexneider, K. I. (2011). Basic examination of blood and bone marrow. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders, 43.
George-Gay, B., & Parker, K. (2003). Understanding the complete blood count with differential. Journal of Perianesthesia Nursing, 18(2), 96-117.
Stone, M. (1999). The Harvard Medical School family health guide.