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Each type of blood cell or element—platelets are fragments of blood cells—plays an important role in how your body works, so all 3 types are studied in a CBC test. Besides these 3 types of cells, blood is also made up of plasma. Plasma is a clear yellow liquid filled with proteins, nutrients, and other substances. Blood cells make up about 45% of your blood. Plasma makes up the rest.

White blood cells come in several varieties, but they all travel around the body via the bloodstream to sites of infection. They help destroy invading bacteria or viruses. White blood cells are measured in thousands per cubic milliliter of blood (K/mm3). Normally, there are fewer white blood cells than red. A normal range of white blood cells may vary slightly from lab to lab, but is roughly 4.0 to 10.0 K/mm3.

Red blood cells are red in color because they contain iron. The iron is in the hemoglobin, a substance that makes it possible for these cells to carry oxygen and carbon dioxide, a waste product. Red blood cells are measured in millions per cubic milliliter of blood (m/mm3). Although the number of red blood cells varies with the altitude at which a person lives. Generally, a normal range of red blood cells is 3.58 to 4.99 m/mm3.

Platelets are the smallest of the blood elements. They are measured in thousands per cubic milliliter (K/mm3). A normal platelet count is about 150 to 450 K/mm3.

This means how much of the blood is red blood cells. Although hematocrit varies with the altitude at which a person lives, generally speaking, a normal hematocrit value for women is 36% to 44%. For men, it is 41% to 50%. The values may be higher for a person living at a high altitude because of the reduced level of oxygen in the atmosphere there.

Neutrophils are the most common white blood cell in the body. They make up about 56% of the white cells in the blood. Their job is to destroy invading bacteria and viruses. On a CBC results sheet, "polys" refers to mature neutrophils and "bands" refers to young neutrophils. Both of these cells are able to fight infection. The CBC also measures absolute neutrophil count (ANC), also known as absolute granulocyte count (AGC). This is the number of disease-fighting white blood cells.

Neutrophils are the first line of defense to fight infections. A normal neutrophil count ranges from 2,500 to 6,000. If your ANC drops to less than 500, you are at serious risk for infection, and this condition is called severe neutropenia. Moderate neutropenia is an ANC between 500 and 1,000. Mild neutropenia is defined as an ANC between 1,000 and 1,500. The risk for infection begins to go up with moderate neutropenia. If you have neutropenia, you need to closely monitor your health and call your healthcare provider at the first sign of illness. Symptoms to watch for include fever, chills, excessive sweating, and frequent urination.

Besides fatigue, other symptoms of anemia include dizziness, shortness of breath, a pounding in the head, pale skin and gums, and a ringing in the ears.

Symptoms of this condition include frequent bruising, tiny red or purple spots on the skin, nosebleeds, bleeding gums, black or bloody stools, and brown or red urine. If you have this condition, you should avoid any medicines containing aspirin, because aspirin interferes with blood clotting. Talk with your doctor about other precautions you should take.