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Red blood cell distribution width (RDW-CV or RCDW and RDW-SD) is a measure of the range of variation of red blood cell (RBC) volume that is reported as part of a standard complete blood count. Usually red blood cells are a standard size of about 6-8 μm in diameter. Certain disorders, however, cause a significant variation in cell size. Higher RDW values indicate greater variation in size. Normal reference range of RDW-CV in human red blood cells is 11.5-14.5%.〔(【引用サイトリンク】url=http://www.fpnotebook.com/hemeonc/lab/RdClDstrbtnWdth.htm )〕 If anemia is observed, RDW test results are often used together with mean corpuscular volume (MCV) results to determine the possible causes of the anemia. It is mainly used to differentiate an anemia of mixed causes from an anemia of a single cause. Deficiencies of Vitamin B12 or folate produce a macrocytic anemia (large cell anemia) in which the RDW is elevated in roughly two-thirds of all cases. However, a varied size distribution of red blood cells is a hallmark of iron deficiency anemia, and as such shows an increased RDW in virtually all cases. In the case of both iron and B12 deficiencies, there will normally be a mix of both large cells and small cells, causing the RDW to be elevated. An elevated RDW (red blood cells of unequal sizes) is known as anisocytosis.〔(The red blood cell distribution width. )〕 An elevation in the RDW is not characteristic of all anemias. Anemia of chronic disease, hereditary spherocytosis, acute blood loss, aplastic anemia (anemia resulting from an inability of the bone marrow to produce red blood cells), and certain hereditary hemoglobinopathies (including some cases of thalassemia minor) may all present with a normal RDW.〔(Table 1.4 in: Kjeldsberg, Carl R.; Perkins, Sherrie L.. Practical Diagnosis of Hematologic Disorders. American Society for Clinical Pathology. ISBN 089189571X. 5th edition. )〕 ==Calculations== The "width" in RDW-CV is sometimes thought of as "misleading," since it in fact is a measure of deviation of the ''volume'' of RBCs, and not directly the diameter. However, "width" refers to the width of the volume curve (distribution width), not the width of the cells. Thus, it is a reasonably accurate term.〔(Pomeranian Medical University > Red blood cell indices (indexes) ) Retrieved on 5 April 2009〕〔(Cornell University, Department of Population Medicine & Diagnostic Sciences > Red Cell Distribution Width (RDW) ) Last Updated: June 2000. Retrieved on 5 April 2009〕 Mathematically the RDW-CV is calculated with the following formula: : RDW-CV = (Standard deviation of MCV ÷ mean MCV) × 100.〔(Encyclopedia of Surgery: A Guide for Patients and Caregivers Red blood cell indices ) Retrieved on 5 April 2009〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Red blood cell distribution width」の詳細全文を読む スポンサード リンク
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