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Number 088
June 7, 2010
Robert Fusco, MD Robert Fusco, MD
Welcome to another e-newsletter from the Center for Digestive Health & Nutrition. Our physicians, nurse practitioner, and registered dietician provide this information to help improve awareness in matters of health and nutrition. Each issue - which now goes out to over 13,000 readers - focuses on a particular topic that we feel will be of interest. I want to thank our readers for their positive feedback and suggestions for future topics.

I'd like to share some information that doctors have about blood tests. We all get them from time to time, but most people really do not understand why they are being done and what the results mean. The topic in this issue of our electronic newsletter is the Complete Blood Count, or CBC. If your doctor does blood tests, you have had this one - probably more than once. If you want some of the mystery unraveled, read on...

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Complete Blood Count (CBC)
What is it?

by Robert Fusco, MD

Okay, you have just seen your family doctor for a checkup. As you leave the office, the nurse says the doctor wants you to have some blood tests as part of your exam. She hands you a laboratory form cryptically marked "CMP and CBC." What do these strange words mean?

Your cells need oxygen
The human body is made up of billions of small cells that are grouped together in the various specialized organs such as the lungs, heart, and liver. These cells work behind the scenes 24/7 to keep you healthy and active. Day and night, they quietly perform many functions such as growth and repair of tissues, production of heat, motion, circulation, digestion, and so forth. Individually, each small cell is much like a tiny machine that requires many things to do its job - including oxygen. The oxygen obviously comes from the air that you breathe. The problem is: How do you deliver oxygen down to each and every cell?

Your bloodstream
The answer lies in your circulatory system, or bloodstream. Your blood stream is a river of fluid called plasma. It is in constant motion pulsing forward within your arteries and veins with each beat of your heart. Floating within this river are several types of living blood cells each with a specific job. Very simply, the CMP (or Complete Metabolic Profile) blood test evaluates the many chemical compounds found in the plasma portion of the blood while the CBC (or Comple Blood Count) evaluates the blood cells themselves. This article will focus on the CBC.

Blood cells are made in the bone marrow. The bone marrow is the soft, spongy tissue found in the center of the large bones. All cells made in the bone marrow start out as a single kind of cell called a stem cell. Depending on what type of cell the body needs, a stem cell can become one of three major types of blood cells: a red cell, a white cell, or a cell that makes platelets. Blood cells must be mature to carry out their jobs properly. The Complete Blood Count (CBC) is a tool your doctor uses to evaluate these three types of cells in your bloodstream.

CELL TYPE ABBREV FUNCTION
Red blood cells RBC Carry oxygen to all parts of the body
White blood cells WBC Fight infection
Platelets PLT Clot your blood when injured

How a CBC is measured
In the past, the components of a CBC had to be manually estimated by viewing a fresh specimen of blood on a microscope slide and counting each cell, a very tedious and time consuming process. During my Medical Internship at Duke University 35 years ago, I spent many sleepless nights staring into a microscope counting the different cells in my patient's blood. Today, automated computerized counting machines can more accurately perform a CBC test in less than a minute.

Today's automated CBC results provide the doctor with 11 different parameters, but when doctors evaluate the results of a patient's CBC, they usually focus on four basic measurements:

WBC = White Blood Cell Count
RBC = Red Blood Cell Count
MCV = Mean Corpuscular Volume
PLT = Platelet Count

White Blood Cell (WBC) count and Differential
White blood cells (also called leukocytes) are your body's mobile defense system against infections. Like a SWAT team, white blood cells travel in the bloodstream to areas of infection and destroy harmful bacteria. A normal WBC count is 4.8 - 10.8 thousand cells per cubic millimeter, but varies from day to day depending upon the circumstances. The WBC count can be temporarily decreased when the body defends itself against a viral infection such as the common cold. A low WBC is an expected side effect of some medications such as Imuran and Purinethol, often used to treat inflammatory bowel disease such as ulcerative colitis and Crohn's disease.

A low WBC count (leukopenia) is the norm during chemotherapy treatments. Like all blood cells, WBCs are made in the bone marrow. Chemotherapy selectively focuses its killing power on rapidly dividing cells, such as cancer cells. That is how it kills cancer cells and not the patient. Unfortunately, the cells in the bone marrow also divide rapidly and are attacked by most chemotherapy agents and the WBC count falls. If it drops too low, chemotherapy is temporarily halted while the bone marrow recovers.

A high WBC count (leukocytosis) is often found when the body is attacked by more serious infections such as bacterial pneumonia or diverticulitis. It is not unusual to see values around 15,000 to 30,000 during a serious bacterial infection. As the infection responds to antibiotic treatment, the WBC count quickly returns to normal. An extreme elevation in the WBC count is seen when cancer of the blood cells develops, a serious condition called leukemia. In this instance the WBC may be well over 100,000.

Not all WBCs are the same. In fact, there are five different types of white blood cells that together make up the total WBC count. Some are better at fighting infection while others focus on supporting the immune system. Others may be involved in allergic reactions. If the doctor orders a CBC with differential, or smear, the lab will break down the WBC count into the different types of white blood cells. This information is sometimes useful in determining the type and severity of an infection, allergic reactions, and other blood disorders.

Red Blood Cell (RBC) level
Red blood cells (also called erythrocytes) have the important job of carrying oxygen from your lungs to all the parts of your body. When you do not have enough red blood cells, you develop a condition called anemia. When severe, anemia can cause symptoms of weakness, easy fatigue, dizziness, pounding in your head, heart palpitations, and shortness of breath.

There are different types of anemia. The most common is due to iron deficiency. More common in women, iron deficiency anemia is often due to pregnancy or heavy menstrual periods. Iron deficiency anemia can also result from slow chronic blood loss from the digestive tract. Strangely, some patients with iron deficiency anemia develop a compulsive craving to eat ice, starch and even dirt. This odd craving, called pica, disappears as the iron is replenished.

More numerous than WBCs, red blood cells are measured in millions per cubic millimeter. A normal RBC count is 3.5 - 5. However, in clinical practice, most doctors use another RBC measurement that is often referred to as the "H & H." This acronym stands for Hemoglobin and Hematocrit, two other ways to monitor the amount of red blood cells in the body.

Hemoglobin is the oxygen carrying protein that gives red blood cells their red color. Hemoglobin allows red blood cells to carry fresh oxygen to the body's cells and to transport carbon dioxide waste back to the lungs where it is exhaled. Hemoglobin is measured in grams per deciliter. A normal HBG is different between the sexes: 14 - 18 gms/dL for men and 12 - 16 gms/dL for women.

Another measurement of red blood cells is the Hematocrit which measures the amount of space that RBCs take up in the blood. This simple test is done by placing fresh unclotted blood in a narrow centrifuge tube, which is spun rapidly, forcing the red blood cells to the bottom of the tube and displacing the plasma to the top. The HCT is reported as a percentage of red blood cells to the total blood volume. A normal HCT is different between the sexes: 42 - 52% for men and 37 - 48% for women.

Mean Corpuscular Volume (MCV)
Mean Corpuscular Volume is a measurement of the average size of your red blood cells. Red blood cells are three-dimensional spheres that have volume. That volume also can be measured and is reported in cubic microns. The normal MCV is around 80 - 100.

A low MCV value means that the red blood cells have shrunk somewhat and are smaller than normal. This is called microcytosis and is often seen in two circumstances - iron deficiency anemia and a hereditary anemia called Thalassemia. A low MCV caused by iron deficiency takes many months to develop and suggests that slow blood loss has been going on for at least several months. Thalassemia is sometimes seen in individuals with a Mediterranean heritage. It can be mild or severe, but taking iron supplements won't help. Less experienced physicians will sometimes mistake the small red blood cells of the person with Thalassemia as a sign of iron-deficiency anemia and incorrectly prescribe iron supplements. A high MCV, or macrocytosis, may be seen in cases of severe deficiency of vitamin B12 or Folic acid. A high MCV is also seen in alcoholics as a toxic effect of alcohol on the bone marrow.

Platelet (PLT) count
Platelets (also called thrombocytes) are the cells that help stop bleeding. When an injury occurs, free-floating platelets quickly clump together to form clotted blood to stop a hemorrhage. Platelets are made in the bone marrow and last about 8 - 10 days in the bloodstream before being replaced. Platelet counts increase during strenuous activity and in certain conditions called myeloproliferative disorders, infections, inflammation, cancers, and when the spleen has been removed. Platelet counts decrease just before menstruation. They are measured in thousands per cubic millimeter. Normal values range from 150,000 to 400,000 per microliter.

When you don't have enough platelets, you have a condition called thrombocytopenia which may lead to easy bruising and increased bleeding from the nose or gums. A count below 50,000 can result in spontaneous bleeding; below 5,000, patients are at risk of severe life-threatening bleeding. This is sometimes seen during chemotherapy. A low PLT count can also be a consequence of an autoimmune reaction when the body mistakenly attacks its own platelets which clump together and are destroyed in the spleen.

Mild elevations in the platelet count called thrombocytosis, may simply be a manifestation of iron deficiency. But, when severe, thrombocytosis can lead to unwanted blood clots inside the body.

Two examples

Summary
The CBC is a common inexpensive screening test that helps the doctor determine your general health status. It is also used to diagnose and monitor a variety of conditions such as infections or anemia. Normal values can vary slightly from laboratory to laboratory. The results of a CBC must be interpreted by the doctor, taking into consideration the age and sex of the patient and any symptoms that may be present. If you have any questions about the results of your CBC, discuss them with your doctor.


Iron Deficiency Anemia

Normal Blood Smear Iron Deficiency Anemia
Iron-containing hemoglobin in your red blood cells (RBC) is what gives your skin a healthy color. Compared to normal, note how pale the red blood cells appear in the patient with iron deficiency. That is why paleness of the skin is a common symptom in those with iron deficiency.


 

 
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