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The results of a CBC can provide information about not only the number of cell types but also can give an indication of the size, shape, and some of the physical characteristics of the cells. In addition, a WBC differential (identifies different types of WBCs) may be ordered and can be done on the same instrument or performed manually.
Significant abnormalities in one or more of the cell populations may require visual confirmation by observing a blood smear under a microscope. In this test, a drop of blood is placed on a glass slide, smeared into a thin layer, allowed to dry, and then dyed with a special stain. A Clinical Laboratory Scientist can then evaluate the physical characteristics of the red and white blood cells present. Any additional information is noted and reported to the doctor.
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 (WBCs)
There are five different types of WBCs that the body uses to maintain a healthy state and to fight infections or other causes of injury. They are neutrophils, lymphocytes, basophils, eosinophils, and monocytes. They are present in the blood at relatively stable percentages. These numbers may temporarily shift higher or lower depending on what is going on in the body. For instance, an infection can stimulate a higher concentration of neutrophils (a “shift to the left”) to fight off bacterial infection. With allergies, there may be an increased number of eosinophils that release certain chemicals (anti-histamines) that minimize the allergic effect. Lymphocytes may be stimulated to produce immunoglobulins (antibodies). And in certain disease states, such as leukemia, abnormal and immature white cells (blasts) rapidly multiply, increasing the WBC count.
Red Blood Cells (RBCs)
RBCs are pale red 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 population of RBCs 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.
How is it used?
The complete blood count or CBC test 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, granulocytes, 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 percentage of red blood cells in a given volume of whole blood.
The 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) as is seen in iron deficiency anemia or thalassemias.
Mean corpuscular hemoglobin (MCH) is a calculation of the average amount of oxygen-carrying hemoglobin inside a red blood cell. Macrocytic RBCs are large so tend to have a higher MCH, while microcytic red cells would have a lower value.
Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the average concentration of hemoglobin inside a red cell. 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 burn patients and 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.
Components of the CBC
TEST NAME INCREASED/DECREASED
WBC White Blood Cell
May be increased with infections, inflammation, cancer, leukemia; decreased with some medications (such as methotrexate), some autoimmune conditions, some severe infections, bone marrow failure, and congenital marrow aplasia (marrow doesn't develop normally)
% Neutrophil Neutrophil/Band/Seg/Gran
Lymphs Lymphocyte
% Mono Monocyte
% Eos Eosinophil
% Baso Basophil
Neutrophil Neutrophil/Ban/Seg/Gran
Lymphs Lymphocyte
Mono Monocyte
Eos Eosinophil
Baso Basophil
This is a dynamic population that varies somewhat from day to day depending on what is going on in the body. Significant increases in particular types are associated with different temporary/acute and/or chronic conditions. An example of this is the increased number of lymphocytes seen with lymphocytic leukemia. For more information, see Blood Smear and WBC.
RBC Red Blood Cell
Decreased with anemia; increased when too many made and with fluid loss due to diarrhea, dehydration, burns
Hgb Hemoglobin Mirrors RBC results
Hct Hematocrit Mirrors RBC results
MCV Mean Corpuscular Volume
Increased with B12 and Folate deficiency; decreased with iron deficiency and thalassemia
MCH Mean Corpuscular Hemoglobin Mirrors MCV results
MCHC Mean Corpuscular Hemoglobin Concentration
May be decreased when MCV is decreased; increases limited to amount of Hgb that will fit inside a RBC
RDW RBC Distribution Width
Increased RDW indicates mixed population of RBCs; immature RBCs tend to be larger
Platelet
Platelet Decreased or increased with conditions that affect platelet production; decreased when greater numbers used, as with bleeding; decreased with some inherited disorders (such as Wiskott-Aldrich, Bernard-Soulier), with Systemic lupus erythematosus, pernicious anemia, hypersplenism (spleen takes too many out of circulation), leukemia, and chemotherapy
MPV Mean Platelet Volume
Vary with platelet production; younger platelets are larger than older ones
Information copy from [ http://labtestsonline.org/understanding/analytes/cbc/tab/sample ]
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