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The Complete Blood Count (CBC) is a very common test that used to be ordered on every person during his or her yearly physical. While it is not run quite as frequently now, it is still used routinely to screen for, help diagnose, and to monitor a variety of conditions, such as anemia and infection.
The CBC is usually carried out as part of a routine medical exam, or as determined by a doctor. It is performed on a blood sample drawn from a vein in the arm or a fingerstick (children and adults) or heelstick (in the case of newborns).
Blood consists of cells suspended in a liquid called plasma. These cells - the RBCs, WBCs, and platelets - are produced and mature primarily in the bone marrow. Under normal circumstances, they are released into the bloodstream as needed.
White Blood Cells (WBC)
There are five different types of WBC that the body uses to fight infections or other causes of injury. These types - neutrophils, lymphocytes, basophils, eosinophils, and monocytes - are present in relatively stable percentages that may temporarily shift higher or lower depending on what is going on in the body. For instance, in the case of an infection, there may be a higher concentration of neutrophils (a "shift to the left"). With allergies, there may be an increased number of eosinophils, and with leukemia, there may be a much higher percentage of a single type of cell, such as a lymphocyte. In this case, the cell may be present in large numbers, in a mature form and in a variety of immature forms. The CBC determines whether there are sufficient WBCs present to fight infection, notes when there are more than expected, and determines the percentages and numbers of each type.
Red Blood Cells (RBC)
RBCs are reddish in color and shaped like a donut with a thinner section in the middle instead of a hole. They have hemoglobin inside them, a protein that transports oxygen throughout the body. The CBC determines whether there are sufficient RBCs present and whether the RBC population appears to be normal. RBCs are normally all the same size and shape; however, variations can occur with vitamin B12 and folate deficiencies, iron deficiency, and with a variety of other conditions. If there are insufficient normal RBCs present, the patient is said to have anemia and may have symptoms, such as fatigue and weakness. Much less frequently, there may be too many RBCs in the blood (erythrocytosis or polycythemia). In extreme cases, this can interfere with the flow of blood through the veins and arteries.
Platelets
Platelets are special cell fragments that play an important role in blood clotting. If a patient does not have enough platelets, he will be at an increased risk of excessive bleeding and bruising. The CBC measures the number and size of platelets present. With some conditions and in some people, there may be giant platelets or platelet clumps that are difficult for the hematology instrument to accurately measure. In this case, a blood smear test may be necessary.
Function; Reasons For Use
The Complete Blood Count (CBC) test is an automated count of the cells in the blood. It provides information about the white blood cell (WBC), red blood cell (RBC), and platelet populations that are present. This information includes the number, type, size, shape, and some of the physical characteristics of the cells. In only a minute or two, the hematology instrument (the machine that is used to run the test) can measure thousands of RBCs, WBCs, and platelets and compare them against established normal ranges. Any abnormalities found are noted, and the clinical laboratory scientist (CLS) running the instrument then uses his or her expertise and experience to accept the automated findings and/or to target the sample for further analysis.
In most cases, the automated CBC is very accurate and the test is complete at this point. If, however, there are significant abnormalities in one or more of the cell populations, a blood smear test may be performed. In this test, a drop of blood is placed on a slide, smeared into a thin layer, allowed to dry, and then dyed with a special stain. A CLS then looks at the slide under the microscope and is able evaluate the cells present. Any additional information is added to that found by the automated count, and all of the findings are reported to the doctor.
The CBC is used as a broad screening test to check for such disorders as anemia, infection, and many other diseases. It is actually a panel of tests that examines different parts of the blood and includes the following:- White blood cell (WBC) count is a count of the actual number of white blood cells per volume of blood. Both increases and decreases can be significant.
- White blood cell differential looks at the types of white blood cells present. There are five different types of white blood cells, each with its own function in protecting us from infection. The differential classifies a person's white blood cells into each type: neutrophils (also known as segs, PMNs, grans), lymphocytes, monocytes, eosinophils, and basophils.
Red blood cell (RBC) count is a count of the actual number of red blood cells per volume of blood. Both increases and decreases can point to abnormal conditions. - Hemoglobin measures the amount of oxygen-carrying protein in the blood.
- Hematocrit measures the amount of space red blood cells take up in the blood. It is reported as a percentage.
- Platelet count is the number of platelets in a given volume of blood. Both increases and decreases can point to abnormal conditions of excess bleeding or clotting. Mean platelet volume (MPV) is a machine-calculated measurement of the average size of your platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced. MPV gives your doctor information about platelet production in your bone marrow.
- Mean corpuscular volume (MCV) is a measurement of the average size of your RBCs. The MCV is elevated when your RBCs are larger than normal (macrocytic), for example in anemia caused by vitamin B12 deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic), such as is seen in iron deficiency anemia or thalassemias.
- Mean corpuscular hemoglobin (MCH) is a calculation of the amount of oxygen-carrying hemoglobin inside your RBCs. Since macrocytic RBCs are larger than either normal or microcytic RBCs, they would also tend to have higher MCH values.
- Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the concentration of hemoglobin inside the RBCs. Decreased MCHC values (hypochromia) are seen in conditions where the hemoglobin is abnormally diluted inside the red cells, such as in iron deficiency anemia and in thalassemia. Increased MCHC values (hyperchromia) are seen in conditions where the hemoglobin is abnormally concentrated inside the red cells, such as in hereditary spherocytosis, a relatively rare congenital disorder.
- Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anemias, such as pernicious anemia, the amount of variation (anisocytosis) in RBC size (along with variation in shape - poikilocytosis) causes an increase in the RDW.
Many patients will have baseline CBC tests to help determine their general health status. If they are healthy and they have cell populations that are within normal limits, then they may not require another CBC until their health status changes or until their doctor feels that it is necessary.
If a patient is having symptoms associated with anemia, such as fatigue or weakness, or has an infection, inflammation, bruising, or bleeding, then the doctor may order a CBC to help diagnose the cause. Significant increases in WBCs may help confirm that an infection is present and suggest the need for further testing to identify its cause. Decreases in the number of RBCs (anemia) can be further evaluated by changes in size or shape of the RBCs to help determine if the cause might be decreased production, increased loss, or increased destruction of RBCs. A platelet count that is low or extremely high may confirm the cause of excessive bleeding or clotting.
Many conditions will result in increases or decreases in the cell populations. Some of these conditions may require treatment, while others will resolve on their own. Some diseases, such as cancer (and chemotherapy treatment), can affect bone marrow production of cells, increasing the production of one cell at the expense of others or decreasing overall cell production. Some medications can decrease WBC counts, and some vitamin and mineral deficiencies can cause anemia. The CBC test may be ordered by the doctor on a regular basis to monitor these conditions and drug treatments.
Expected Outcome
It is important to note that a standard reference range is not available for this test. Because reference values are dependent on many factors, including patient age, gender, sample population, and test method, numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test.
Some tests provide a simple yes-or-no answer. Was the culture positive for strep throat? Did the test find antibodies to a virus that indicates an infection?
But for many more tests, the meaning of the results depends on their context. A typical lab report will have your results followed by a normal or reference range. For example, your results for a thyroid-stimulating hormone (TSH) test might look something like: 2.0 m-IU/L, ref range 0.5-5.0 m-IU/L. The test results indicate that it falls within the "normal" range.
Laboratories will generally report your test results accompanied by a reference range keyed to your age and sex. Your physician then will still need to interpret the results based on personal knowledge of your particulars, including any medications or herbal remedies you may be taking. A plethora of additional factors can affect your test results: your intake of caffeine, tobacco, alcohol, and vitamin C; your diet (vegetarian vs. omnivorous); stress or anxiety; or a pregnancy. Even your posture when the sample is taken can affect some results, as can recent heavy exertion. For example, albumin and calcium levels may increase when shifting from lying down to an upright position.
What can be done about a bad CBC result?
Patients who have a keen interest in their own healthcare frequently want to know what they can do to change their WBCs, RBCs, and platelets. Unlike "good" and "bad" cholesterol, cell populations are not generally affected by lifestyle changes unless the patient has an underlying deficiency (such as vitamin B12 or folate deficiency or iron deficiency). There is no way that a patient can directly raise the number of his WBCs or change the size or shape of his RBCs. Addressing any underlying diseases or conditions and following a healthy lifestyle will help optimize your body's cell production and your body will take care of the rest.
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CBC (Complete Blood Count) Test can help with the following:
KEY | | Highly recommended |
GLOSSARY
Allergy (Allergies)
Hypersensitivity caused by exposure to a particular antigen (allergen), resulting in an increased reactivity to that antigen on subsequent exposure, sometimes with harmful immunologic consequences.
Anemia (Anaemia, Anemias)
A condition resulting from an unusually low number of red blood cells or too little hemoglobin in the red blood cells. The most common type is iron-deficiency anemia in which the red blood cells are reduced in size and number, and hemoglobin levels are low. Clinical symptoms include shortness of breath, lethargy and heart palpitations.
Antibody (Antibodies)
A type of serum protein (globulin) synthesized by white blood cells of the lymphoid type in response to an antigenic (foreign substance) stimulus. Antibodies are complex substances formed to neutralize or destroy these antigens in the blood. Antibody activity normally fights infection but can be damaging in allergies and a group of diseases that are called autoimmune diseases.
Anxiety
Apprehension of danger, or dread, accompanied by nervous restlessness, tension, increased heart rate, and shortness of breath unrelated to a clearly identifiable stimulus.
Arterial (Arteries, Artery)
Blood that leaves the heart. When it leaves the right ventricle, it is venous blood; and when it leaves the left ventricle, through the aorta, it is fresh and oxygenated. After it has passed out to the capillaries and started to return, it is venous blood.
Basophil (Basophils)
The basophils account for about 1% of the granulocyte count (60 to 75% of the white blood cells). They release chemicals such as histamine and play a role in the inflammatory response to infection.
Bruise (Bruised, Bruising)
Injury producing a hematoma or diffuse extravasation of blood without breaking the skin.
Calcium
The body's most abundant mineral. Its primary function is to help build and maintain bones and teeth. The body also needs calcium to carry nerve signals, keep the heart functioning, contract muscles, clot blood and maintain healthy skin. Calcium helps control blood acid-alkaline balance, plays a role in cell division, muscle growth and iron utilization, activates certain enzymes, and helps transport nutrients through cell membranes. Calcium also forms a cellular cement called ground substance that helps hold cells and tissues together.
Cancer
Refers to the various types of malignant neoplasms that contain cells growing out of control and invading adjacent tissues, which may metastasize to distant tissues.
Chemotherapy
A treatment of disease by any chemicals. Used most often to refer to the chemical treatments used to combat cancer cells. Chemotherapy is usually given in cycles: a treatment period followed by a recovery period, then another treatment period, and so on. Most anticancer drugs are given by injection into a blood vessel (IV); some are given by mouth. Chemotherapy is a systemic therapy, meaning that the drugs enter the bloodstream and travel throughout the body. Usually, a patient has chemotherapy as an outpatient (at the hospital, at the doctor's office, or at home). However, depending on which drugs are given and the patient's general health, a short hospital stay may be needed.
Cholesterol
A waxy, fat-like substance manufactured in the liver and found in all tissues, it facilitates the transport and absorption of fatty acids. In foods, only animal products contain cholesterol. An excess of cholesterol in the bloodstream can contribute to the development of atherosclerosis.
Cobalamin (B12, B-12, Cobalamine, Vitamin B12)
Essential for normal growth and functioning of all body cells, especially those of bone marrow (red blood cell formation), gastrointestinal tract and nervous system, it prevents pernicious anemia and plays a crucial part in the reproduction of every cell of the body i.e. synthesis of genetic material (DNA).
Complete Blood Count (CBC)
A set of measurements that are generally determined by specially designed machines that analyze the different components of blood in less than a minute. The values generally included are:- White blood cell count (WBC). The number of white blood cells in a volume of blood. Normal range varies slightly between laboratories but is generally between 4,300 and 10,800 cells per cubic millimeter. This can also be referred to as the leukocyte count and can be expressed in international units as 4.3 - 10.8 x 10^9 cells per liter.
- Automated white cell differential. A machine-generated percentage of the different types of white blood cells, usually split into granulocytes, lymphocytes, monocytes, eosinophils, and basophils.
- Red cell count (RBC). The number of red blood cells in a volume of blood. Normal range varies slightly between laboratories but is generally between 4.2 - 5.9 million cells per cubic millimeter. This can also be referred to as the erythrocyte count and can be expressed in international units as 4.2 - 5.9 x 10^12 cells per liter.
- Hemoglobin (Hb). The amount of hemoglobin in a volume of blood. Normal range for hemoglobin is different between the sexes and is approximately 13 - 18 gm/dl for men and 12 - 16 for women (international units 8.1 - 11.2 millimoles/liter for men, 7.4 - 9.9 for women).
- Hematocrit (Hct). The ratio of the volume of red cells to the volume of whole blood. Normal range for hematocrit is different between the sexes and is approximately 45 - 52% for men and 37 - 48% for women.
- Mean cell volume (MCV). The average volume of a red cell. This is a calculated value derived from the hematocrit and red cell count. Normal range is 86 - 98 femtoliters.
- Mean cell hemoglobin (MCH). The average amount of hemoglobin in the average red cell. This is a calculated value derived from the measurement of hemoglobin and the red cell count. Normal range is 27 - 32 picograms.
- Mean cell hemoglobin concentration (MCHC). The average concentration of hemoglobin in a given volume of red cells. This is a calculated volume derived from the hemoglobin measurement and the hematocrit. Normal range is 32 - 36%.
- Red cell distribution width (RDW). A measurement of the variability of red cell size. Higher numbers indicate greater variation in size. Normal range is 11 - 15.
- Platelet count. The number of platelets in a volume blood. Platelets play a vital role in blood clotting. Normal range varies slightly between laboratories but is in the range of 150,000 - 400,000 per cubic millimeter (150 - 400 x 10^9 per liter).
Eosinophil (Eosinophilia, Eosinophils)
The eosinophils, ordinarily about 2% of the granulocyte count (60 to 75% of the white blood cells), increase in number in the presence of allergic disorders and parasitic infestations.
Hemoglobin
The oxygen-carrying protein of the blood found in red blood cells.
Herbs (Herb, Herbal)
Herbs may be used as dried extracts (capsules, powders, teas), glycerites (glycerine extracts), or tinctures (alcohol extracts). Unless otherwise indicated, teas should be made with one teaspoon herb per cup of hot water. Steep covered 5 to 10 minutes for leaf or flowers, and 10 to 20 minutes for roots. Tinctures may be used singly or in combination as noted. The high doses of single herbs suggested may be best taken as dried extracts (in capsules), although tinctures (60 drops four times per day) and teas (4 to 6 cups per day) may also be used.
Hormones (Hormone)
Chemical substances secreted by a variety of body organs that are carried by the bloodstream and usually influence cells some distance from the source of production. Hormones signal certain enzymes to perform their functions and, in this way, regulate such body functions as blood sugar levels, insulin levels, the menstrual cycle, and growth. These can be prescription, over-the-counter, synthetic or natural agents. Examples include adrenal hormones such as corticosteroids and aldosterone; glucagon, growth hormone, insulin, testosterone, estrogens, progestins, progesterone, DHEA, melatonin, and thyroid hormones such as thyroxine and calcitonin.
Iron
An essential mineral. Prevents anemia: as a constituent of hemoglobin, transports oxygen throughout the body. Virtually all of the oxygen used by cells in the life process are brought to the cells by the hemoglobin of red blood cells. Iron is a small but most vital, component of the hemoglobin in 20,000 billion red blood cells, of which 115 million are formed every minute. Heme iron (from meat) is absorbed 10 times more readily than the ferrous or ferric form.
Leukemia
Cancer of the lymph glands and bone marrow resulting in overproduction of white blood cells (related to Hodgkin's disease).
Lymphocyte
A type of white blood cell found in lymph, blood, and other specialized tissue such as bone marrow and tonsils, constituting between 22 and 28 percent of all white blood cells in the blood of a normal adult human being. B- and T-lymphocytes are crucial components of the immune system. The B-lymphocytes are primarily responsible for antibody production. The T-lymphocytes are involved in the direct attack against living organisms. The helper T-lymphocyte, a subtype, is the main cell infected and destroyed by the AIDS virus.
Mineral (Minerals)
Plays a vital role in regulating many body functions. They act as catalysts in nerve response, muscle contraction and the metabolism of nutrients in foods. They regulate electrolyte balance and hormonal production, and they strengthen skeletal structures.
Neutrophils (Neutrophil)
Another name for polymorphonuclear leukocytes, the most common type of blood-carried white blood cell, and the first mobile resistance cell to come to the rescue in injury.
Pernicious Anemia
Anemia caused by a vitamin B12 deficiency.
Platelets (Platelet)
Cells that help the blood to clot.
Protein (Proteins)
Compounds composed of hydrogen, oxygen, and nitrogen present in the body and in foods that form complex combinations of amino acids. Protein is essential for life and is used for growth and repair. Foods that supply the body with protein include animal products, grains, legumes, and vegetables. Proteins from animal sources contain the essential amino acids. Proteins are changed to amino acids in the body.
Red Blood Cell (Erythrocyte, Erythrocytes, RBC, Red Blood Cells)
Any of the hemoglobin-containing cells that carry oxygen to the tissues and are responsible for the red color of blood.
Spherocytosis (Spherocytes)
A disease of the blood characterized by the production of red blood cells (erythrocytes), that are sphere-shaped, rather than donut-shaped. It is caused by a molecular defect in one or more of the proteins of the red blood cell cytoskeleton. Because the cell skeleton has a defect, the blood cell contracts to its most surface-tension efficient and least flexible configuration, a sphere, rather than the more flexible donut-shape. The sphere-shaped red blood cells are known as spherocytes.
Streptococcus (Strep)
A genus of gram-staining chain-forming cocci bacteria. Some are responsible for common and potentially serious human infections, ranging from scarlet fever and strep throat to bacterial endocarditis and pus pockets. Most of the disease-potential streps are also a normal part of the skin, mouth and upper respiratory flora.
Thalassemia
An inherited form of anemia occurring chiefly among people of Mediterranean descent, caused by faulty synthesis of part of the hemoglobin molecule.
Vegetarian (Lacto-Ovo-Vegetarian, Vegetarianism, Vegetarians)
A person who consumes no meat, fish or fowl (chicken, turkey, etc.), but who may consume animal products such as dairy products (milk, cheese, butter, etc.), eggs or honey.
Virus (Viri, Viruses)
Any of a vast group of minute structures composed of a protein coat and a core of DNA and/or RNA that reproduces in the cells of the infected host. Capable of infecting all animals and plants, causing devastating disease in immunocompromised individuals. Viruses are not affected by antibiotics, and are completely dependent upon the cells of the infected host for the ability to reproduce.
Vitamin C (Ascorbic Acid)
A water-soluble antioxidant vitamin essential to the body's health. When bound to other nutrients, for example calcium, it would be referred to as "calcium ascorbate". As an antioxidant, it inhibits the formation of nitrosamines (a suspected carcinogen). Vitamin C is important for maintenance of bones, teeth, collagen and blood vessels (capillaries), enhances iron absorption and red blood cell formation, helps in the utilization of carbohydrates and synthesis of fats and proteins, aids in fighting bacterial infections, and interacts with other nutrients. It is present in citrus fruits, tomatoes, berries, potatoes and fresh, green leafy vegetables.
White Blood Cell (WBC, White Blood Cells)
A blood cell that does not contain hemoglobin: a blood corpuscle responsible for maintaining the body's immune surveillance system against invasion by foreign substances such as viruses or bacteria. White cells become specifically programmed against foreign invaders and work to inactivate and rid the body of a foreign substance. White blood cells are composed primarily of neutrophils, monocytes and lymphocytes. Lymphocytes are either T-cells or B-cells. T-cells (CD3 cells) are divided into T-helper (CD4 cells) and T-suppressor/cytotoxic (CD8 cells) cells.
Last updated: May 11, 2008
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