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Red cell distribution width (RDW) is a measurement of the size variation of RBCs. In some anemias, including pernicious anemia, the variation calculated value (anisocytosis) in RBC size (along with variation in shape poikilocytosis) causes a rise in the RDW.
RDW is a result of dividing the standard deviation (SD) by the mean corpuscle volume (MCV) and then multiplying that result by 100. The standard deviation shows the volume of erythrocytes or red blood cells that present in the blood smear. The RDW calculation equation is: RDW=SD/MCV x 100.
Commonly a standard size of red blood cells is about 6-8µm. However, some diseases cause a significant variation in cell size. Elevated RDW values indicate greater declination in size. When anemia is diagnosed, RDW test results are examined together with mean corpuscular volume (MCV) results to identify the cause of the anemia. It is mostly used to distinguish an anemia of mixed causes from an anemia of a single cause. A macrocytic (large cell) anemia can be produced by vitamin B12 deficiency with a normal RDW. But iron deficiency anemia basically found with a varied size distribution of red blood cells, and as such shows high RDW. In the case of a mixed iron and B12 deficiency, there can be a mixture of both large cells and small cells, causing the increased RDW. High RDW, called anisocytosis, presents red blood cells of unequal sizes.
It does not make a sense to consider the RDW aspect of a blood test without including MCV. Mean corpuscle value (MCV) goes in cooperation with red-blood cell-distribution width (RDW) in terms of anemia and other hematology diseases, and the levels of both are affected by each other. For instance, decreased MCV value in combination with normal RDW can signifies a chronic disorder, while decreased MCV reading in conjunction with decreased RDW can point to iron deficiency. In the same respect, a normal MCV in conjunction with normal RDW can represent a chronic disease and normal MCV combined with high RDW can indicate a B12 deficiency. Also when MCV levels are high and RDW is normal, pre-leukemia can be found. Both increased MCV and increased RDW can point to folate deficiency.
Anisocytosis is diagnosed when the RDW levels in a blood test signify abnormally elevated values of variably shaped red blood cells. The presence of anisocytosis in a diagnostic blood test is so common that it is frequently dismissed as a component while making a diagnosis. When anisocytosis is calculated against other blood cells levels, the increased RBC levels may help make a better determination of the type of anemia that is present in the patient.
Anisocytosis is a medical term meaning that a patient's red blood cells are of unequal size. This is found in anemia and other blood conditions. False diagnostic flagging may be triggered by an elevated WBC count, agglutinated RBCs, RBC fragments, giant platelets or platelet clumps. The red cell distribution width (RDW) is a measurement of anisocytosis. Increased RDW is seen in iron deficiency anemia, Thalassemia Major (Cooley's anemia), Thalassemia Intermedia and myelodysplastic syndromes.
All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.