Since RDW-CV is mathematically derived from MCV, it is therefore affected by the average RBC size (MCV). RDW-CV = (1 standard deviation of RBC volume ÷ MCV) × 100%. RDW-CV (expressed in %) is calculated with the following formula: This parameter is, therefore, not influenced by the average RBC size ( mean corpuscular volume, MCV).

RDW-SD is calculated as the width (in fL) of the RBC size distribution histogram at the 20% height level. However, 'width' refers to the width of the volume curve (distribution width), not the width of the cells. The 'width' in RDW is sometimes thought to be 'misleading', since it in fact is a measure of deviation of the volume of RBCs, and not directly the diameter. 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. Īn elevation in the RDW is not characteristic of all anemias. An elevated RDW (red blood cells of unequal sizes) is known as anisocytosis. In the case of both iron and B 12 deficiencies, there will normally be a mix of both large cells and small cells, causing the RDW to be elevated. 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. It is mainly used to differentiate an anemia of mixed causes from an anemia of a single cause.ĭeficiencies of Vitamin B 12 or folate produce a macrocytic anemia (large cell anemia) in which the RDW is elevated in roughly two-thirds of all cases. 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. Normal reference range of RDW-CV in human red blood cells is 11.5–15.4%. Higher RDW values indicate greater variation in size. Certain disorders, however, cause a significantly increased variation in cell size. Red blood cells have an average volume of 80-100 femtoliters, but individual cell volumes vary even in healthy blood. Red blood cell distribution width ( RDW), as well as various types thereof ( 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. Measure of the range of variation of red blood cell volume that is reported as part of a standard complete blood count.

Test viscosity of hemoglobin in rbc