Red blood cell distribution width

<h2 id="calculations">Calculations</h2>
<p>The "width" in RDW is sometimes thought to be "misleading", since it in fact is a measure of deviation of the <i>volume</i> of RBCs, and not directly the diameter. RDW-CV "width" refers to the width of the volume curve (distribution width), not the width of the cells. 
<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p><p>RDW-SD is calculated as the width (in fL) of the RBC size distribution histogram at the 20% height level. This parameter is, therefore, not influenced by the average RBC size (<a href="/facts/Mean_corpuscular_volume/jou11aso">mean corpuscular volume</a>, MCV).<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
</p><p>RDW-CV (expressed in %) is calculated with the following formula:
</p>
RDW-CV = (1 <a href="/facts/Standard_deviation/qSug9BRl">standard deviation</a> of RBC volume ÷ MCV) × 100%.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a>
<p>Since RDW-CV is mathematically derived from MCV, it is therefore affected by the average RBC size (MCV).<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>
</p>
<h2 id="pathological-implications">Pathological implications</h2>
<h3>Normal RDW</h3>
<p>Anemia in the presence of a normal RDW may suggest <a href="/facts/Thalassemia/NF7GIJsJ">thalassemia</a>. A low <a href="/facts/Mentzer_index/kEupvCXs">Mentzer Index</a>, calculated from CBC data [MCV/RBC < 13], may suggest this disorder but a hemoglobin electrophoresis would be diagnostic. Anemia of chronic diseases show normal RDW.
</p>
<h3>High RDW</h3>
<p>High RDW may be a result of the presence of fragments, groups of agglutination, and/or abnormal shape of red blood cells.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a>
</p>
<ul><li>Iron-deficiency anemia usually presents with high RDW and low MCV.</li>
<li>Folate and vitamin B12 deficiency anemia usually presents with high RDW and high MCV.</li>
<li>Mixed-deficiency (iron + B12 or folate) anemia usually presents with high RDW and variable MCV.</li>
<li>Recent hemorrhages typically present with high RDW and normal MCV.</li>
<li>A false high RDW reading can occur if <a href="/facts/EDTA/XvHgKQyD">EDTA</a> anticoagulated blood is used instead of citrated blood.  See <a href="/facts/Pseudothrombocytopenia/mCerMa0o">Pseudothrombocytopenia</a>.</li></ul>
<p>By severity, elevated RDW can be classified as follows:
</p>
<table><tbody><tr><th>RDW in adults<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a></th><th>Severity<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a></th><th>Most notable causes<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a></th></tr><tr><th>14.5% - 18%</th><td>Mild anisocytosis</td><td>Infection, vigorous exercise or certain drugs. <a href="/facts/Iron_deficiency_anemia/LK17js79">Iron deficiency anemia</a> in the presence of anemia and microcytosis.</td></tr><tr><th>18% - 26%</th><td>Moderate anisocytosis</td><td>Severe iron deficiency anemia, <a href="/facts/Megaloblastic_anemia/Ru2zwG6C">megaloblastic anemia</a>.</td></tr><tr><th>> 26%</th><td>Severe anisocytosis</td><td>Sideroblastic anemia</td></tr></tbody></table>

<h2 id="further-reading">Further reading</h2>
<ul><li><a href="https://web.archive.org/web/20180806155333/http://rdwbloodtest.com/">RDW Blood Test - Red Blood Cell Distribution Width</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Nah EH, Kim S, Cho S, Cho HI (November 2018). "Complete Blood Count Reference Intervals and Patterns of Changes Across Pediatric, Adult, and Geriatric Ages in Korea". Annals of Laboratory Medicine. 38 (6): 503–511. doi:10.3343/alm.2018.38.6.503. PMC 6056383. PMID 30027692. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Nah EH, Kim S, Cho S, Cho HI (November 2018). "Complete Blood Count Reference Intervals and Patterns of Changes Across Pediatric, Adult, and Geriatric Ages in Korea". Annals of Laboratory Medicine. 38 (6): 503–511. doi:10.3343/alm.2018.38.6.503. PMC 6056383. PMID 30027692. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Red Cell Distribution Width". Family Practice Notebook. Retrieved 18 October 2013. <a href="http://www.fpnotebook.com/hemeonc/lab/RdClDstrbtnWdth.htm" target="_blank">http://www.fpnotebook.com/hemeonc/lab/RdClDstrbtnWdth.htm</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Nah EH, Kim S, Cho S, Cho HI (November 2018). "Complete Blood Count Reference Intervals and Patterns of Changes Across Pediatric, Adult, and Geriatric Ages in Korea". Annals of Laboratory Medicine. 38 (6): 503–511. doi:10.3343/alm.2018.38.6.503. PMC 6056383. PMID 30027692. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056383</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Evans TC, Jehle D (1991). "The red blood cell distribution width". The Journal of Emergency Medicine. 9 (Suppl 1): 71–4. doi:10.1016/0736-4679(91)90592-4. PMID 1955687. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Kjeldsberg CR, Perkins SL (2010). "Table 1.4". Practical Diagnosis of Hematologic Disorders (5th ed.). Chicago, IL: ASCP Press. ISBN 978-0-89189-571-8. Archived from the original on 25 July 2013. <a href="978-0-89189-571-8" target="_blank">978-0-89189-571-8</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Pomeranian Medical University > Red blood cell indices (indexes)[permanent dead link‍] Retrieved on 5 April 2009 <a href="http://www.ams.edu.pl/files/File/wronog/Metodyki-unit_4c.pdf" target="_blank">http://www.ams.edu.pl/files/File/wronog/Metodyki-unit_4c.pdf</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Cornell University, Department of Population Medicine & Diagnostic Sciences > Red Cell Distribution Width (RDW) Last Updated: June 2000. Retrieved on 5 April 2009 <a href="http://diaglab.vet.cornell.edu/clinpath/modules/hemogram/rdw.htm" target="_blank">http://diaglab.vet.cornell.edu/clinpath/modules/hemogram/rdw.htm</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Curry, Choladda Vejabhuti (7 January 2017). "Red Cell Distribution Width (RDW): Reference Range, Interpretation, Collection and Panels". Medscape Reference. Retrieved 18 May 2019. <a href="https://emedicine.medscape.com/article/2098635-overview" target="_blank">https://emedicine.medscape.com/article/2098635-overview</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
<li id="fn:10"><p>Encyclopedia of Surgery: A Guide for Patients and Caregivers Red blood cell indices Retrieved on 5 April 2009 <a href="http://www.surgeryencyclopedia.com/Pa-St/Red-Blood-Cell-Indices.html" target="_blank">http://www.surgeryencyclopedia.com/Pa-St/Red-Blood-Cell-Indices.html</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li>
<li id="fn:11"><p>Curry, Choladda Vejabhuti (7 January 2017). "Red Cell Distribution Width (RDW): Reference Range, Interpretation, Collection and Panels". Medscape Reference. Retrieved 18 May 2019. <a href="https://emedicine.medscape.com/article/2098635-overview" target="_blank">https://emedicine.medscape.com/article/2098635-overview</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li>
<li id="fn:12"><p>Curry, Choladda Vejabhuti (7 January 2017). "Red Cell Distribution Width (RDW): Reference Range, Interpretation, Collection and Panels". Medscape Reference. Retrieved 18 May 2019. <a href="https://emedicine.medscape.com/article/2098635-overview" target="_blank">https://emedicine.medscape.com/article/2098635-overview</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li>
<li id="fn:13"><p>"High RDW level in the blood". MrLabTest. Last update: 12/01/2021 <a href="https://www.mrlabtest.com/high-RDW-blood.htm" target="_blank">https://www.mrlabtest.com/high-RDW-blood.htm</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li>
<li id="fn:14"><p>"High RDW level in the blood". MrLabTest. Last update: 12/01/2021 <a href="https://www.mrlabtest.com/high-RDW-blood.htm" target="_blank">https://www.mrlabtest.com/high-RDW-blood.htm</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li>
<li id="fn:15"><p>"High RDW level in the blood". MrLabTest. Last update: 12/01/2021 <a href="https://www.mrlabtest.com/high-RDW-blood.htm" target="_blank">https://www.mrlabtest.com/high-RDW-blood.htm</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li>
</ol>

Red blood cell distribution width open-in-new

Red blood cell distribution width