Understanding White Blood Cells and Differentials

Every one of the trillions of cells in your body has a specific task. The primary job of white blood cells (WBCs), sometimes called leukocytes, is to help fight invaders, such as bacteria and viruses.

It all begins inside the bones where there is a red, spongy area known as the marrow. This is where pre-existing cells divide and specialize to become the blood. Stem cells in the bone marrow can produce red blood cells (RBCs), platelets, or a variety of WBCs.

A sample of blood, even one as small as a drop, looks red. If you take that sample of blood, place it in a small tube, and spin it very fast for several minutes, you will see three layers. The bottom later has a deep red color and consists primarily of red blood cells, comprising about 45% of the total volume. The top layer is the golden-colored plasma, which is about 54% of the total volume. Plasma is a complex solution of water, salts, wastes, vitamins, proteins, fats, sugars, etc.

The remaining 1% of the blood is seen as a thin, murky, white middle layer between the red blood cells below and the plasma above. This narrow band consists mainly of platelets and WBCs.

WBCs are not white at all, but the white appearance of this layer explains the name given to this cell type. To understand white blood cells further, we look at them using a microscope with special stains as the cells are laid out (smeared) on a glass slide. When you have a complete blood count or a WBC with a “differential,” the cells can be identified under a microscope and counted.

There are three main types of WBCs – granulocytes, lymphocytes, and monocytes.

Granulocytes

Granulocytes include basophils, eosinophils, and neutrophils, categorized this way because of their color and the presence of tiny granules seen when the sample is stained in the laboratory:

• Basophils are the smallest in number, and account for 0-2% of the total number of WBCs. Their granules contain histamine, which is a potent chemical in allergic reactions. They also contain heparin, a chemical that prevents the clotting of blood. Basophils are a first line of defense as they engulf and destroy infectious organisms.

• Eosinophils are more numerous, making up 0-8% of the total. Their granules contain proteins that can kill bacteria and parasites. These proteins also play a role in inflammation, a common bodily reaction to illness or injury.

• Neutrophils are the most numerous of all the WBCs, comprising 40% to 80% of the total number of WBCs. Their granules contain a potent enzyme that directly attacks bacteria. Interestingly, neutrophils also have cell projections that can lay down “traps” to snare infectious organisms and devour them.

Lymphocytes

Lymphocytes are quite common among the WBCs, comprising 15-49% of the total number. There are two groups of lymphocytes including B-cells and T-cells. Unlike the other immune cells, the B-cells and T-cells can adapt to new infections and help the immune system fight infections. They also play a vital role in remembering previous infections. And some types of T-cells naturally kill cancerous cells that grow in the body as well.

Monocytes

Monocytes are the largest cells in the blood stream, making up 0-13% of the total number of WBCs. They too can engulf and devour infectious cells, but they can also help to repair the surrounding body cells that have been damaged by the infection. In addition to devouring invading cells, monocytes display fragments of the dead cells to the outside to help the lymphocytes “learn” more about the infecting cells.

As soon as an invader – or pathogen – enters the body, the immune system begins a race to expel the pathogens before they become too numerous. The WBCs respond by multiplying rapidly as well. The change in the numbers of WBCs usually signals that the immune system is responding to the bacteria, viruses, fungi, or parasites that have entered the body.

Some of these pathogens can quickly overwhelm the body’s defenses. If that happens, the lymphocytes can then mount a specific response that is very effective at destroying these infection-causing organisms or even providing a more rapid response when a second infection occurs, sometimes even decades after the first.

WBCs are usually measured as part of a simple blood test called a complete blood count, commonly called a CBC. The part of the CBC that looks at the WBCs measures both the number of WBCs as well as the breakdown for each type of WBC type and that is called the “differential.”

A blood test measuring WBCs may be used to identify types and stages of blood cancers, like leukemia. In addition, checking WBCs can help to detect any infections and their severity.

Patient Power asked George D Lundberg, MD, a leading academic pathologist, medical journalist, and current Editor in Chief of Cancer Commons, to explain more about WBCs and cancer.

Dr. Lundberg said that “cancer treatment itself, such as radiation or chemotherapy, often disturbs the WBCs, perhaps lowering them a lot. That makes a patient less capable of resisting infections.” As a result, it is important to keep track of WBC levels to measure the response to cancer treatment as well as to monitor the risk of infection.

What are expected WBC values? Dr. Lundberg explained that “so-called ‘normal’ is a statistical reference range determined by testing large numbers of individuals. Each person is an individual and may carry different, but consistent, numbers over a lifetime. But most lab results offer a “range” of normal results. Typically, a WBC count groups all the types together with one number, with the total ranging from about 4,000-11,000/microliter of blood. A "differential" breaks these WBCs down by the percentage of each type seen.

Dr. Lundberg said that, with any cancer, concern is reasonable when WBC numbers change substantially (either higher or lower), from a person’s usual counts. That’s why it is vital to be in touch with your physician about your own personal results.

He added that, “since blood cancers involve the white cells and may involve the red cells as part of the cancer, the ups and downs of numbers vary all over the place, depending on blood cancer types and stages. This may reflect good or bad news, on a case-to-case basis.”