Erythrocyte distribution width

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The erythrocyte distribution width (EVB), which is also often referred to in German-speaking countries with the English abbreviation RDW ( Red Blood Cell Distribution Width ), is a parameter that is determined in laboratory medicine as part of a blood count . The measurement of the EVB, which is given in percent and is a measure of the size distribution of the red blood cells (erythrocytes) in the blood , is carried out by means of flow cytometry . It is calculated from the standard deviation of the volume (S v ) of the red blood cells ( erythrocytes ) and the mean value of the erythrocyte volume (MCV) according to the formula

The size distribution of red blood cells in healthy patients corresponds to one of about six to nine micrometers in diameter extending normal distribution bell curve , which according to the English pathologist Cecil Price-Jones as a Price-Jones curve is known. Its maximum is around 120 out of 500 cells at around 7.5 micrometers. The normal thickness of the red blood cells, which are shaped as concave round disks, is around two micrometers on the edge and around one micrometer in the center. The EVB is mainly dependent on the diameter of the red blood cells and thus partially correlates with the width of the Price-Jones curve. In addition, the thickness of the red blood cells also has an influence on the EVB. It describes the uneven distribution ( anisocytosis ) of the erythrocytes in shape and size.

The reference range for the EVB is approximately 11.5 to 14.5 percent, depending on the laboratory normal value. Highly elevated values ​​are an indication of the presence of various forms of anemia , such as hemolytic anemia , iron deficiency anemia , pernicious anemia or spheroidal cell anemia . In addition, if the reference range is significantly exceeded, this can also indicate osteomyelofibrosis . However, an increased finding is usually not considered in isolation, but is used in connection with other laboratory values ​​for differential diagnosis . Values ​​below the reference range, however, have no clinical relevance. In general, the EVB is not given great importance in everyday clinical practice.

literature

  • EVB - width of erythrocyte distribution. In: Rolf Mahlberg, Annette Gilles, Anita Läsch: Hematology: Theory and Practice for Medical Assistant Professions. Wiley-VCH, Weinheim 2005, ISBN 3-527-31185-8 , p. 148
  • Ayalew Tefferi: Primary Hematology. Humana Press, Totowa NJ 2000, ISBN 0-89603-664-2 , p. 8

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