{"id":"rdw-sd","name":"Red Cell Distribution Width (RDW-SD)","shortName":"RDW-SD","aliases":["RDW-SD","Red Cell Distribution Width - SD","Red Cell Dist Width SD","RDW-SD (fL)","RDW SD","Red Cell Distribution Width-SD","Red Cell Distribution Width (RDW-SD)","Red Blood Cell Distribution Width SD","RDW-SD (fl)","RDW (SD)","Red Cell Dist Width-SD","Red Cell Distribution Width Standard Deviation","Erythrocyte Distribution Width SD"],"abbreviations":["RDW-SD","RDW SD"],"loinc":[{"code":"115742-9","primary":true},{"code":"21000-5","primary":false},{"code":"30384-2","primary":false}],"specimen":"whole-blood","units":[{"ucum":"fL","display":"fL"},{"ucum":"um3","display":"µm³"}],"referenceRanges":[{"population":"Adults","low":37.4,"high":52.4,"unit":"fL","unitDisplay":"fL","note":"Vanderbilt Medical Laboratories prints 37.4–52.4 fL for all ages and both sexes on its Sysmex analyzers (March 2024). RDW-SD limits depend on the analyzer and the population, and published limits vary: OHSU Laboratory Services prints 35.1–46.3 fL for all ages and both sexes (2018 document), and healthy Russian adults measured on Beckman Coulter analyzers had 37.7–45.5 fL. In a Cameroon study of healthy adults on a URIT 3300 analyzer, the manufacturer's range was 37–54 fL, but the local healthy range was 24.8–43.7 fL for men and 24.2–44.3 fL for women. Values tend to rise with age (Clin Chem Lab Med 2015; Wuhan 2020), and the Wuhan study found higher values in women, while the 2015 study found no sex difference. RDW-SD (fL) is a separate result from RDW-CV (%), with different ranges. Use the range printed on your own report.","sources":[{"title":"Sysmex Complete Blood Count Reference Ranges (March 2024)","url":"https://www.testmenu.com/vanderbiltmedicallabs/TestDirectory/SiteFile?fileName=sidebar%5CVML%20Operations%20Sysmex%20Complete%20Blood%20Count%20Reference%20Ranges.pdf","publisher":"Vanderbilt Medical Laboratories","year":2024},{"title":"Heme Reference Ranges (updated 6/5/18)","url":"https://www.ohsu.edu/sites/default/files/2019-07/cbcrefrange.pdf","publisher":"OHSU Laboratory Services (Oregon Health & Science University)","year":2018},{"title":"Derivation of Russian-specific reference intervals for complete blood count, iron markers and related vitamins","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC11441669/","publisher":"PLoS One","year":2024},{"title":"Establishment of Hematological Reference Values among Healthy Adults in Bamenda, North West Region of Cameroon","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC7932772/","publisher":"Anemia","year":2021},{"title":"Reference intervals of systemic immune-inflammation index, neutrophil to lymphocyte ratio, platelet to lymphocyte ratio, mean platelet volume to platelet ratio, mean platelet volume and red blood cell distribution width-standard deviation in healthy Han adults in Wuhan region in central China","url":"https://pubmed.ncbi.nlm.nih.gov/32673141/","publisher":"Scandinavian Journal of Clinical and Laboratory Investigation","year":2020},{"title":"Effect of age and gender on reference intervals of red blood cell distribution width (RDW) and mean red cell volume (MCV)","url":"https://pubmed.ncbi.nlm.nih.gov/26536583/","publisher":"Clinical Chemistry and Laboratory Medicine","year":2015}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"How wide the spread of red blood cell sizes is, in femtoliters (fL). A higher number means a wider mix of small and large cells.","url":"https://bloodtesttracker.com/markers/rdw-sd","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}