Medical

Ask the Nurse Karen Morin, RN OCN

I know my health care team is checking my blood frequently, why and what does the blood count mean?

Understanding Blood Counts

Blood cells come from the bone marrow, a spongy layer that is found inside the long and flat bones of the body, for example the long bones of the arms and legs, the breast bone, the shoulder blades and the pelvic bones. The bone marrow provides a home to protect immature blood cells (or stem cells) as they grow and develop into mature cells. When cells are fully mature and able to do their normal job, they are released from the marrow to circulate in the blood stream.

Cancer cells reproduce more rapidly than normal cells and divide in an abnormal way in the body. Treatments, such as chemotherapy and radiation therapy can destroy cancer cells by preventing cells from growing and dividing in a number of different ways. Your blood count may become temporarily low during treatment because neither radiotherapy nor chemotherapy distinguishes between growing cancer cells or normal cells. White cell differential count, sometimes referred to as a "diff," measures the proportion of the total white cell count that is composed of one of the five principal white cell types. The observer can also tell if the white cells in the blood are normal in appearance. The A blood sample is used to count - literally - the numbers of mature blood cells in the circulation. Doctors are mostly interested in the number of white blood cells, red blood cells and platelets that you have. There are several different types of white cells, all of which function in various ways to protect the body from infection.

A group of white cells called neutrophils, for example, protect the body by destroying microbes and bacteria They produce pus and help to alert you to the fact that an infection may be present, for example by causing pain, swelling and redness. White blood cells are important as they provide your body's main protection against infection. When the number of white cells, specifically neutrophils, is low, this is called neutropenia The five types of normal white cells that are counted are neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Blood contains about 60% neutrophils, 30% lymphocytes, 5% monocytes, 4% eosinophils and 1% basophils. Having a low white blood cell count means that you have very few white cells in circulation. This can make it unsafe to give chemotherapy because of the risk of infection. When your white cell count is very low, simple infections that you would normally shrug off can become very serious very quickly. For this reason, it is very important that you alert your doctor or nurse if you have a temperature or feel unwell.

Platelets help your blood to clot. You have seen how when you cut your finger the bleeding stops after a short while. This happens because platelets stick together and form a "plug". In just the same way as you would use a plug to keep water in the sink, platelets are there to keep the blood in our arteries and veins by stopping any leaks if we damage ourselves. However, platelets have a slightly longer life span than white cells, so it is a little less likely to see severe drops in numbers in the blood count. On average, platelets live for about a week, so bone marrow replaces them by dividing from week to week - the daily demand is not as high as it is for white cells. There are about 1400 million platelets in your blood stream - lots more than white cells.

Since platelets are designed to stop us from bleeding, you might notice that you bruise more easily or more commonly that your gums bleed more than normal when you brush your teeth. There are no medicines that can help your platelet count to recover but if you needed one, you could have a transfusion of platelets. A low level of platelets in the blood stream is called thrombocytopenia.

Red blood cells give the blood its deep red color. Their most important role is to carry oxygen around the body. Oxygen is needed by every cell in the body and red blood cells transport it to them. If the number of red blood cells is low, then less oxygen is circulated and you may begin to feel tired, short of breath or light-headed. Red cells live for about 3 - 4 months and therefore the marrow doesn't need to divide very often to make new ones. For this reason, although some may be destroyed by treatment, it usually takes several courses of chemotherapy before your red cells become affected. When the number of red cells is low, this is known as anemia. In most cases, blood counts are usually at their lowest about 7-14 days after chemotherapy. Before having a further cycle of chemotherapy, your blood count will be checked to see if it has recovered sufficiently and it is safe to give you chemotherapy. If the blood count is still low, your team may recommend postponing your treatment for a short time (usually a few days or a week) until your blood count has recovered. Sometimes, it is necessary to give you a small injection, or course of injections, under your skin to stimulate the production of blood cells in your bone marrow. These injections are called "growth factors" and have very few side effects.

A blood count allows your team to check how many blood cells you have available, and to decide whether you can receive your next course of chemotherapy safely. Very importantly, the blood count also helps to decide whether you need antibiotic treatment to prevent or fight infection, a platelet transfusion to prevent bleeding, or a red blood cell transfusion to help you feel better and have more energy.