Complete Blood Count (CBC)

One of the most common types of lab tests (Read about "Laboratory Testing") you can have is a complete blood count or CBC. A CBC is designed to look at three types of cells that are circulating in your blood: red blood cells, white blood cells and platelets. The National Institutes of Health (NIH) say these blood cells are made in the bone marrow, the spongy tissue filling the center of your bones. Bone marrow in the skull, sternum (breastbone), ribs, vertebral column (backbone) and pelvis produces these blood cells.

Each type of blood cell plays a role in keeping us healthy and allowing our bodies to function. A complete blood count provides these five measurements:

• white blood cell (WBC) count - White blood cells fight infections. (Read about "The Immune System")
• red blood cell (RBC) count - Red blood cells carry oxygen to and remove waste products from the body's tissues. These cells also contain hemoglobin.
• hemoglobin (HGB) value - Hemoglobin gives red blood cells their color. Hemoglobin carries oxygen from the lungs to the tissues and takes carbon dioxide (the waste products) from the tissues to the lungs. From the lungs, carbon dioxide is exhaled. (Read about "Respiratory System")
• hematocrit (HCT) value - The hematocrit is the percentage of red blood cells in relation to your total blood volume.
• platelet count - Platelets help to stop bleeding by forming blood clots.

A blood sample is needed for a CBC. The sample is taken by a needle placed in a vein in the arm or by a fingerstick. In infants, a heel stick can be used to obtain a blood sample. The site is first cleaned with an antiseptic before the needle is used. The blood is usually drawn into a tube that contains an anticoagulant to keep the blood from clotting.

Ranges

For each measurement in a complete blood count, there is a normal range. This range can vary depending on age and sex. This is based on tests performed on healthy individuals. Your lab report should include the specific reference range for your tests. These are what are considered normal levels. You should discuss your test results with your doctor.

What it all means

If your any part of your blood count falls outside the normal range, it can indicate illness or it can cause other problems, according to NIH. To understand that, you need to understand exactly what each part of your blood does and how it affects your health.

White blood cells

These cells are the mobile units of the body's infection-fighting system. (Read about "The Immune System") White blood cells travel in the bloodstream to areas of infection and destroy the responsible microorganism. (Read about "Microorganisms") However, the WBC value is not always meaningful unless the differential is also known. The differential measures each of the five types of white blood cells. The Leukemia & Lymphoma Society says the types of white blood cells are:

• neutrophils (polys and bands)
• lymphocytes
• monocytes
• eosinophils
• basophils

Neutrophils are the most numerous white blood cells. Neutrophils are the "soldiers" that fight infections. They eat or gobble up the infectious particles in your body. On your test results, you may see the words "polys" and "bands." Polys are mature neutrophils; bands are young polys, which also fight infections.

The absolute neutrophil count (ANC), also called absolute granulocyte count (AGC), is the measure of the number of infection-fighting white blood cells in your blood, according to NIH. The American Association for Clinical Chemistry (AACC) says if you have a high number of white blood cells, it can indicate a number of conditions such as infections, inflammation, cancer and leukemia. (Read about "Cancer: What It Is" "Leukemia") When you have a low number of neutrophils, your risk of infection is increased. This condition is called neutropenia. It can result from, among other things, medications, autoimmune diseases, some severe infections and bone marrow failure, according to AACC. If you are neutropenic and develop a fever or signs of infection, contact your doctor immediately.

AACC says that many normal things can impact a WBC differential, things as common as eating, exercise and stress. (Read about "Stress") Certain drugs and chemicals, such as steroids can also result in differential issues.

Red blood cells

When you do not have enough red blood cells, you develop a condition called anemia. (Read about "Anemia") When you are anemic, your hematocrit and/or hemoglobin levels will be below normal. You may feel weak and tired, and you may also have these symptoms:

• dizziness
• shortness of breath
• heart palpitations (racing heartbeat)
• pounding in your head
• ringing in your ears (Read about "Tinnitus")

You may be advised to change your diet if you are anemic. You may also need blood transfusions if your hematocrit or hemoglobin is too low. If you lose fluids because of burns, diarrhea or dehydration it can result in elevated levels of red blood cells. (Read about "Burn Prevention" "Diarrhea" "Dehydration")

Platelets

When you do not have enough platelets, you have a condition called thrombocytopenia. (Read about "Bleeding Disorders") You may bruise easily, and you may also have some of the following signs:

• tiny, pinpoint-sized red or purple spots on your skin (petechiae)
• nose bleeds
• bleeding gums
• prolonged bleeding from a cut
• black or bloody stool
• brown or red urine
• increased vaginal bleeding.

Many over-the-counter drugs contain aspirin, and aspirin prevents platelets from working as they should. Speak with your doctor before taking medication. (Read about "Medicine Safety") AACC says your platelet count can also be low because of excess bleeding, conditions such as lupus, pernicious anemia, leukemia and chemotherapy. (Read about "Lupus" "Anemia" "Leukemia" "Cancer Treatments")