Complete Blood Count

Description
A complete blood count (CBC) is a common blood test, providing information on general health status and is a tool for checking disorders such as anemia, infection and thrombocytopenia. CBC provides detailed information about three types of cells including white blood cells (WBC), red blood cells (RBC), and platelets. All of which may be increased or decreased with various conditions.

“WBC may be increased with infections, inflammation, cancer, leukemia, and decreased with some medications (such as methotrexate), some autoimmune conditions, some severe infections, bone marrow failure, and congenital marrow aplasia. RBC is decreased with anemia, and increased when too many made and with fluid loss due to diarrhea, dehydration, and burns. Platelet may be decreased or increased with conditions that affect platelet production, and decreased when greater numbers used, as with bleeding, with some inherited disorders (such as Wiskott-Aldrich, Bernard-Soulier), and with systemic lupus erythematosus, pernicious anemia, and hypersplenism” (http://www.labtestsonline.org/understanding/analytes/cbc/test.html).

There is a panel of tests that that examine different parts of the blood. The following information is from the Medical Laboratory Services Website (http://www.mlsstjames.com/pages/tests/cbc.htm).

The white blood cell (WBC) count is a count of the number of white blood cells per volume of blood. Both increases and decreases can be significant. Depending on the laboratory's report forms, white blood cells are reported as thousands in a microliter of blood (for example 5,000/µL or 5.0x103/µL) or as millions in a liter of blood (5.0x109/L).

The 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 providing protection 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.

The red blood cell (RBC) count is a count of the number of red blood cells per volume of blood. Both increases and decreases can point to abnormal conditions. Depending on the laboratory's report forms, red blood cells are reported as millions in a microliter of blood (4,250,000/µL or 4.25x106/µL) or as millions in a liter of blood (4.25x1012/L).

Hemoglobin measures the amount of oxygen-carrying protein in the blood. The Hematocrit test (Hct, Crit, Packed cell volume) measures the amount of space red blood cells taken up in the blood. It is reported as a percentage.

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. Depending on the laboratory's report forms, platelets are reported as thousands in a microliter of blood (150,000/µL or 150.0x103/µL) or as millions in a liter of blood (150.0x109/L).

Mean platelet volume (MPV) is a machine-calculated measurement of the average size of platelets. New platelets are larger, and an increased MPV occurs when increased numbers of platelets are being produced. MPV provides information about platelet production in bone marrow.

Mean corpuscular volume (MCV) is a measurement of the average size of the red blood cells (RBC). The MCV is elevated when RBC is larger than normal (macrocytic), for example in anemia caused by vitamin B12 deficiency. When the MCV is decreased, RBC is smaller than normal (microcytic) such as is seen in iron deficiency anemia.

Mean corpuscular hemoglobin (MCH) is a calculation of the amount of oxygen-carrying hemoglobin inside RBC. Since macrocytic RBC is larger than either normal or microcytic RBC, it would also tend to have higher MCH values.

Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the percentage of hemoglobin in the RBC. Decreased values point to hypochromasia, decreased oxygen-carrying capacity because of decreased hemoglobin inside the cell. Hypochromasia is seen in iron deficiency anemia and in thalassemia.

Red cell distribution width (RDW) is a calculation of the variation in the size of RBCs. In some anemias, such as pernicious anemia, the amount of variation (anisocytosis) in RBC size (along with variation in shape – poikilocytosis) may help evaluate the severity of a condition.

Significance of Measurement
Studies have shown that elevated white blood cell count is associated with increased risk for ischemic heart disease (Yarnell et al., 1991), CHD (Ensrud & Grimm, 1992; Lee et al., 2001; Packard et al., 2000; Weijenberg, Feskens, & kromhout, 1996), ischemic stroke (Lee et al., 2001), and mortality (Lee et al., 2001; Weijenberg, Feskens, & kromhout, 1996).

Method of Measurement
The CBC is performed on a blood sample taken by a needle placed in a vein in the arm or by a fingerstick
(http://www.labtestsonline.org/understanding/analytes/cbc/sample.html).

References
· Ensrud, K., & Grimm, R.H. (1992). The white blood cell count and risk for coronary heart disease. American Heart Journal,124, 207-213.
· Lab Tests Online. (2005.). Complete blood count. Retrieved March 23, 2005, from(http://www.labtestsonline.org/understanding/analytes/cbc/test.html) (http://www.labtestsonline.org/understanding/analytes/cbc/sample.html).
· Lee, C.D., Folsom, A., Nieto, F.J., Chambless, L.E., Shahar, E., & Wolfe, D.A. (2001). White blood cell count and incidence of coronary heart disease and ischemic stroke, and mortality from cardiovascular disease in African-American and White men and women: The Atherosclerosis Risk in Communities Study. American Journal of Epidemiology, 154(8), 758-764.
· Medical Laboratory Services. (2003). Complete blood count CBC. Retrieved March 23, 2005, from http://www.mlsstjames.com/pages/tests/cbc.htm
· Packard, C.J., O'Reilly, D.S, Caslake, M.J., McMahon, A.D., Ford, I., Cooney, J., et al. (2000). Lipoprotein-associated phospholipase A2 as an independent predictor of coronary heart disease. West of Scotland Coronary Prevention Study Group. New England Journal of Medicine, 343(16), 1148-1155.
· Weijenberg, M.P., Feskens, E.J.M., & Kromhout, D. (1996). White blood cell count and the risk of coronary heart disease and all-cause mortality in elderly men. Arteriosclerosis, Thrombosis, and Vascular Biology,16, 499-503.
· Yarnell, J.W., Baker, I.A., Sweetnam, P.M., Bainton, D., O'Brien, J.R., Whitehead, P.J., et al. (1991). Fibrinogen, viscosity, and white blood cell count are major risk factors for ischemic heart disease. The Caerphilly and Speedwell Collaborative Heart Disease Studies. Circulation, 83, 836-844.