Red blood cell distribution width - wikipedia Red blood cell distribution width Human red blood cells Red blood cell distribution width ( RDW or 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 %. 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 B 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 B 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. 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. Contents 1 Calculations 2 Pathological Implications 2.1 Normal RDW 2.2 High RDW 3 References Calculations The `` width '' in RDW - CV 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. However, `` width '' refers to the width of the volume curve ( distribution width, here presented as the Coefficient of Variation, or CV ), not the width of the cells. Thus, it is a reasonably accurate term. Mathematically, the RDW - CV is calculated with the following formula : RDW - CV = ( Standard deviation of MCV ÷ MCV ) × 100. Pathological implications Normal RDW Anemia in the presence of a normal RDW may suggest thalassemia. A low Mentzer Index, calculated from CBC data, may suggest this disorder but a hemoglobin electrophoresis would be diagnostic. High RDW Iron - deficiency anemia usually presents with high RDW and low MCV. Folate - and vitamin B12 - deficiency anemia usually present with high RDW and high MCV. Mixed - deficiency ( iron + B12 or folate ) anemia usually presents with high RDW and variable MCV. Recent hemorrhages typically present with high RDW and normal MCV. A false high RDW reading can occur if EDTA anticoagulated blood is used instead of citrated blood. See Pseudothrombocytopenia. References Jump up ^ `` Red Cell Distribution Width ''. Family Practice Notebook. Retrieved 18 October 2013. Jump up ^ Evans TC, Jehle D ( 1991 ). `` The red blood cell distribution width ''. J Emerg Med. 9 Suppl 1 : 71 -- 4. doi : 10.1016 / 0736 - 4679 ( 91 ) 90592 - 4. PMID 1955687. Jump up ^ Table 1.4 in : Kjeldsberg, Carl R. ; Perkins, Sherrie L... Practical Diagnosis of Hematologic Disorders. American Society for Clinical Pathology. 5th edition. Archived 2013 - 07 - 25 at the Wayback Machine... ISBN 089189571X Jump up ^ Pomeranian Medical University > Red blood cell indices ( indexes ) Retrieved on 5 April 2009 Jump up ^ Cornell University, Department of Population Medicine & Diagnostic Sciences > Red Cell Distribution Width ( RDW ) Last Updated : June 2000. Retrieved on 5 April 2009 Jump up ^ Encyclopedia of Surgery : A Guide for Patients and Caregivers Red blood cell indices Retrieved on 5 April 2009 7. http://rdwbloodtest.com Red Blood Cell Distribution Width Myeloid blood tests ( CPT 85002 -- 85999 ) Clotting CBC Platelet count Mean platelet volume vWF : Ristocetin - induced platelet aggregation clotting factors : Prothrombin time Partial thromboplastin time Thrombin time Activated clotting time other / general : coagulation Bleeding time animal enzyme Reptilase time Ecarin clotting time Dilute Russell 's viper venom time Thromboelastography Thrombodynamics test fibrinolysis : Euglobulin lysis time D - dimer Red blood cell indices CBC RBC count Hematocrit Hemoglobin ratios : Mean corpuscular hemoglobin Mean corpuscular hemoglobin concentration Mean corpuscular volume Red blood cell distribution width Fetal hemoglobin : Apt -- Downey test Kleihauer -- Betke test Other Reticulocyte index Haptoglobin Mentzer index CFU - GM Nitro blue tetrazolium chloride test Complete blood count Absolute neutrophil count Other Blood film Blood viscosity Erythrocyte sedimentation rate Retrieved from `` https://en.wikipedia.org/w/index.php?title=Red_blood_cell_distribution_width&oldid=850333763 '' Categories : Blood tests Hidden categories : Webarchive template wayback links All articles with dead external links Articles with dead external links from April 2018 Articles with permanently dead external links Talk Contents About Wikipedia Deutsch Español Français Hrvatski Italiano Nederlands Polski Português Srpskohrvatski / српскохрватски ไทย 3 more Edit links This page was last edited on 15 July 2018, at 06 : 10 ( UTC ). 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Question: what is an rdw in a blood test
Answer: measure of the range of variation of red blood cell (RBC) volume that is reported as part of a standard complete blood count