Red Cell Distribution Width - Coefficient of Variation (RDWCV)
RDWCV is a hematological parameter calculated by dividing the standard deviation of red blood cell volume by the mean corpuscular volume (MCV) and multiplying by 100 to express the result as a percentage, with normal values typically ranging from 11.0-14.0%. 1, 2
Definition and Calculation
- RDWCV quantifies the heterogeneity (variation) in the size of circulating erythrocytes, providing a numerical measure of anisocytosis 2
- The formula for RDWCV is: (Standard deviation of RBC volume ÷ MCV) × 100% 1
- Normal RDWCV is generally considered to be less than or equal to 14.0%, corresponding to the 95th percentile in reference populations 2
Clinical Significance
- RDWCV is traditionally used in the differential diagnosis of anemias, particularly in distinguishing between different types of microcytic anemias 3, 4
- When combined with low MCV (microcytosis), an elevated RDWCV strongly suggests iron deficiency anemia 1, 5
- A normal RDWCV with microcytosis may suggest thalassemia, though this distinction is not absolute 2, 6
- RDWCV can help identify iron deficiency when microcytosis and macrocytosis co-exist, resulting in a normal MCV 2
Interpretation in Different Clinical Contexts
- Iron deficiency progression correlates with increasing RDWCV values:
- Normal individuals: 12.7 ± 0.7%
- Prelatent iron deficiency: 13.2 ± 0.8%
- Latent iron deficiency: 14.0 ± 1.5%
- Iron deficiency anemia: 15.6 ± 1.7% 5
- When combined with normal MCV, an elevated RDWCV may indicate early iron deficiency, vitamin B12 or folate deficiency, or hemolysis 1
- RDWCV has emerged as a prognostic marker in various cardiovascular and cerebrovascular diseases 7, 4
Clinical Application
- RDWCV should always be interpreted alongside other hematologic parameters including hemoglobin, MCV, and other red cell indices 2
- In suspected iron deficiency, confirmation with serum ferritin (<30 μg/L without inflammation, <100 μg/L with inflammation) is recommended 1
- Minimum workup for abnormal RDWCV should include complete blood count with MCV, reticulocyte count, serum ferritin, transferrin saturation, and CRP 1
Common Pitfalls to Avoid
- Assuming iron deficiency based solely on microcytosis without checking RDWCV 1
- Attributing microcytosis to thalassemia in certain ethnic groups without laboratory confirmation 3
- Overlooking the possibility of combined deficiencies (e.g., iron and B12), which may result in a normal MCV despite abnormal RDWCV 1, 2
- Failing to recognize that almost half of thalassemia cases may present with increased RDWCV, limiting its specificity in differentiating from iron deficiency 6
Emerging Research
- Recent evidence suggests that increased RDWCV is associated with decreased RBC deformability, which can impair blood flow through the microcirculation 8
- RDWCV is now being regarded as a strong and independent risk factor for mortality in the general population 4
- The mechanisms underlying these associations may involve oxidative stress, inflammation, poor nutritional status, and alterations in erythropoiesis 4