Anemia Biomarker
Collection Type: Blood
Related System: Anemia
Red cell distribution width coefficient of variation (RDW-CV) is a measure of the variation in size (volume) of circulating red blood cells (anisocytosis). It is calculated from the red cell histogram of a complete blood count (CBC) and expressed as a percentage. RDW-CV helps detect and characterize different types of anemia for example, iron-deficiency, vitamin B12/folate deficiency, hemolytic anemias, mixed deficiencies, and some bone‑marrow disorders. Symptoms prompting testing include fatigue, pallor, shortness of breath, weakness, or unexplained bruising. RDW can vary slightly with age (tends to increase in older adults), pregnancy, and certain chronic illnesses; gender differences are minimal. Interpretation requires correlation with hemoglobin, mean corpuscular volume (MCV) and clinical context.
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Q: What does RDW CV being high mean?
A: RDW‑CV (red cell distribution width—coefficient of variation) measures variation in red blood cell size. A high RDW‑CV means increased size variability (anisocytosis), commonly caused by iron deficiency, vitamin B12 or folate deficiency, recent bleeding, hemolysis, mixed nutritional deficiencies, or bone marrow disorders. It helps differentiate anemia types and may signal chronic disease or inflammation; follow‑up testing is usually needed to find the cause.
Q: What infection causes high RDW?
A: Elevated RDW is seen with infections that disrupt red blood cell production or cause hemolysis. Examples include malaria and other hemolytic infections, chronic infections such as HIV and hepatitis C, and severe systemic infections or sepsis. Inflammation and bone marrow suppression during these infections lead to anisocytosis (variable RBC size), producing a raised RDW.
Q: What to eat if RDW is high?
A: High RDW often reflects nutritional deficiencies. Eat iron-rich foods red meat, poultry, fish, legumes, tofu, dark leafy greens and pair them with vitamin C foods (citrus, bell peppers, tomatoes) to boost absorption. Include folate (leafy greens, beans, fortified cereals) and B12 (eggs, dairy, fish, fortified products). Avoid tea/coffee with meals. See a clinician for tests and tailored supplements if needed.
Q: Can dehydration cause high RDW?
A: Dehydration itself typically does not cause an elevated RDW. RDW reflects red blood cell size variation (anisocytosis), which increases with iron, B12/folate deficiency, hemolysis, mixed anemias, bone marrow stress or recent transfusion. Severe hemoconcentration may alter some CBC values, so rehydrate and repeat testing if results are unexpected, and discuss findings with your clinician.
Q: What is the most common cause of high red blood cell count?
A: The most common cause of a high red blood cell count is secondary polycythemia from chronic low oxygen (hypoxia). Conditions such as chronic lung disease (COPD), smoking, obstructive sleep apnea, or living at high altitude increase erythropoietin production and raise red cell mass. Less commonly, erythropoietin‑producing tumors or primary marrow disorders (polycythemia vera) are responsible.
Q: Can dehydration cause high RDW?
A: Dehydration typically causes hemoconcentration but does not directly increase RDW. RDW reflects red blood cell size variation (anisocytosis) and most often rises with iron, B12/folate deficiency, hemolysis, recent transfusion, or bone marrow disorders. Severe dehydration can subtly alter lab values, so recheck a CBC after rehydration and discuss persistent high RDW with your clinician to identify underlying causes.