What is Red Cell Distribution Width - Coefficient of Variation (RDWCV)?

Red Cell Distribution Width - Coefficient of Variation (RDWCV)

RDWCV is a calculated hematologic parameter that measures the variation in red blood cell size, expressed as a percentage, calculated by dividing the standard deviation of red blood cell volume by the mean corpuscular volume (MCV) and multiplying by 100. 1, 2

Definition and Calculation

• RDWCV is calculated using the formula: RDW (%) = (Standard deviation of red blood cell volume / MCV) × 100 1
• Normal RDWCV values are typically less than or equal to 14.0%, which corresponds to the 95th percentile in reference populations 2
• The value obtained depends on the specific laboratory instrument used, so results should be interpreted according to the laboratory's reference range 1

Clinical Significance

• RDWCV helps assess the degree of anisocytosis (variation in red blood cell size) in the peripheral blood 2, 3
• It is traditionally used in the differential diagnosis of anemias but has applications beyond hematological disorders 3
• When combined with MCV, RDWCV provides valuable diagnostic information:
  • Low MCV + High RDWCV (>14.0%): Suggests iron deficiency anemia 1, 2
  • Low MCV + Normal RDWCV (≤14.0%): Suggests thalassemia minor 1, 2
  • Normal MCV + High RDWCV: May indicate early iron deficiency, vitamin B12/folate deficiency, or mixed anemia 2

Role in Iron Deficiency Diagnosis

• RDWCV shows larger values as iron deficiency progresses, even before microcytosis becomes evident 4
• The sensitivity of RDWCV for diagnosing iron deficiency anemia is approximately 77.1%, with a specificity of 90.6% 4
• RDWCV often increases before changes in MCV become apparent, making it an early indicator of developing iron deficiency 2

Expanded Clinical Applications

• Beyond anemia diagnosis, elevated RDWCV has been identified as a predictor of morbidity and mortality in various conditions:
  • Cardiovascular diseases 5, 6, 7
  • Venous thromboembolism 3
  • Cancer 3
  • Respiratory conditions (pneumonia, COPD) 3
  • Liver and kidney failure 3
• An increased RDWCV may reflect underlying biological and metabolic imbalances including:
  • Inflammation 2, 3
  • Oxidative stress 3, 7
  • Poor nutritional status 3
  • Erythrocyte fragmentation 3
  • Alteration of erythropoietin function 3

Interpretation in Clinical Practice

• RDWCV should always be interpreted alongside other hematologic parameters (hemoglobin, MCV, reticulocyte count) 2
• Even with normal RDWCV, if anemia is present, further investigation is warranted 2
• When clinical suspicion for iron deficiency exists despite normal RDWCV, additional tests like serum ferritin and transferrin saturation should be considered 2

Common Pitfalls

• RDWCV values can vary between different laboratory instruments, so values should be interpreted according to the specific laboratory's reference range 1, 2
• Elevated RDWCV is not specific to any single condition and should be interpreted in clinical context 2, 3
• In mixed deficiency states (e.g., concurrent iron and folate deficiency), the expected RDWCV pattern may be altered 1, 2