RDW, RDW-SD and RDW-CV

Q: What's the difference between RDW, RDW-SD and RDW-SC?

Answer: 

Red cell distribution width (RDW) signifies either microcytosis (low RDW) or macrocytosis (high RDW). The two major causes of microcytosis, probably accompanied by hypochromia, are thalassemia and iron deficiency.

RDW- Standard Deviation (RDW-SD) measures the actual variation in size of red blood cells. A high RDW-SD means cells vary significantly in size. RDW-SD is an actual, physical measurement of the cell volume distribution curve at a level 20% above the baseline of the histogram.

RDW — Coefficient of Variation (RDW-CV) is a calculation influenced by average red blood cell size. It is usually considered less precise than RDW-SD because it measures the histogram at the midpoint.

RDW-SD, RDW-CV, and Mean Corpuscular Volume (MCV) should be read together for better understanding. 

#hematology

#laboratory science

References:

1. Sarma PR. Red Cell Indices. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 152. Available from: https://www.ncbi.nlm.nih.gov/books/NBK260/

2. Salvagno GL, Sanchis-Gomar F, Picanza A, Lippi G. Red blood cell distribution width: A simple parameter with multiple clinical applications. Crit Rev Clin Lab Sci. 2015;52(2):86-105. doi: 10.3109/10408363.2014.992064. Epub 2014 Dec 23. PMID: 25535770.

3. Yang K, Sun B, Zhang S, Pan Y, Fang J. RDW-SD is Superior to RDW-CV in Reflecting Liver Fibrosis Stage in Patients with Chronic Hepatitis B. Infect Drug Resist. 2023 Oct 27;16:6881-6891. doi: 10.2147/IDR.S427047. PMID: 37920477; PMCID: PMC10619233.