Red Cell Distribution Width (RDW)
Red cell distribution width measures the variation in red blood cell size. RDW increases with age in both sexes, reflecting greater heterogeneity in red cell production.
Unit: % · 12 slices · age and sex · 1 source
Filed under panels: Complete Blood Count · topics: Hematology
Red cell distribution width (RDW) is the coefficient of variation of red blood cell volume, expressed as a percentage. A higher RDW indicates greater variability in cell size (anisocytosis). RDW increases with age and is influenced by iron status, nutritional deficiencies, and chronic disease. It is often interpreted alongside MCV to narrow the differential for anemia.
Population Distribution
Browse by Demographic
| Age (years) | male (%) | female (%) |
|---|---|---|
| 20-29 | 12.4–14.6 (13) | 12.2–16.1 (13.2) |
| 30-39 | 12.4–14.9 (13.2) | 12.4–16.1 (13.3) |
| 40-49 | 12.4–15 (13.3) | 12.5–17.2 (13.6) |
| 50-59 | 12.4–15 (13.5) | 12.3–16.6 (13.5) |
| 60-69 | 12.7–15.6 (13.6) | 12.6–15.6 (13.6) |
| 70+ | 12.6–16.3 (13.8) | 12.8–16.6 (13.9) |
Frequently Asked Questions
Why does RDW increase with age?
Older adults have more heterogeneous red cell populations due to subclinical nutritional deficiencies, chronic disease, and less uniform bone marrow output. This produces a wider spread of cell sizes.
What does RDW add to MCV?
MCV is an average. Two populations can have the same average cell size but different amounts of variation. RDW captures that variation. For example, early iron deficiency may raise RDW before MCV drops, because a mix of normal and small cells increases variability while the average is still normal.
Why do females tend to have slightly higher RDW than males?
Iron deficiency is more prevalent in premenopausal females due to menstrual blood loss, and iron deficiency produces a mixed population of normal and small red cells that widens RDW. After menopause the sex difference in RDW narrows, consistent with this explanation.