CBC Biomarker
Collection Type: Blood
Related System: CBC
Red cell distribution width (RDW) is a laboratory measure of the variation (anisocytosis) in red blood cell (RBC) size. It is calculated from the red cell histogram on a complete blood count (CBC) and reported as RDW‑CV (%) and/or RDW‑SD (fL). RDW helps distinguish types of anemia and detect mixed nutritional deficiencies (iron, B12, folate), hemolysis, recent transfusion effects, marrow disorders, and chronic disease. Symptoms prompting testing include fatigue, pallor, shortness of breath, dizziness, or unexplained weakness. RDW can vary with age (infants and older adults often differ), pregnancy, and to a lesser extent by sex; reference ranges may also differ slightly by laboratory.
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Symptom Checker11.5-14.5% (RDW‑CV) OR 39-46 fL (RDW‑SD)
Q: What does it mean if your RDW is high?
A: A high RDW means there’s increased variation in red blood cell size (anisocytosis). It’s commonly seen with iron deficiency, vitamin B12 or folate deficiency, recent blood loss, hemolysis, chronic liver disease, or mixed anemias. It’s a nonspecific finding that prompts further tests—MCV, iron studies, B12/folate, reticulocyte count—and clinical assessment to identify the underlying cause and guide treatment.
Q: What if RDW is more than 14?
A: If RDW is above ~14%, it indicates increased variation in red blood cell size (anisocytosis). Causes include iron, B12 or folate deficiency, recent bleeding, hemolysis, liver disease or mixed anemias. Your clinician will usually repeat the CBC, examine a peripheral smear and order iron studies, B12/folate, reticulocyte count and hemolysis markers to find the cause and guide treatment. Follow-up with your doctor is recommended.
Q: What cancers cause high RDW?
A: Elevated RDW has been reported in many cancers: colorectal, lung, breast, gastric, hepatocellular, pancreatic and ovarian cancers, as well as hematologic malignancies (leukemia, lymphoma, myelodysplastic syndromes). It’s also described in renal cell carcinoma, esophageal cancer and multiple myeloma. RDW is a nonspecific marker reflecting inflammation, nutritional deficiency or bone‑marrow dysfunction and often correlates with worse prognosis.
Q: How to treat high RDW in blood test?
A: Treating high RDW focuses on the underlying cause. Common steps: test for iron, B12, folate, thyroid and inflammatory markers; replace deficiencies (iron, B12, folic acid) and adopt iron-rich dietary changes; treat chronic disease, infections or bleeding; review medications; and refer to a hematologist if unexplained or severe. Follow-up CBCs monitor response. Discuss results and a tailored plan with your healthcare provider.
Q: What is the condition of high RDW?
A: High RDW (red cell distribution width) means increased variation in red blood cell size (anisocytosis). It often signals nutritional deficiencies (iron, B12, folate), recent bleeding, hemolysis, chronic inflammation, liver disease, or bone marrow disorders. It’s a laboratory clue rather than a diagnosis; clinicians interpret RDW with hemoglobin, MCV, reticulocyte count and iron/B12/folate tests to find the underlying cause and guide treatment.
Q: What infection causes high RDW?
A: Severe infections—especially sepsis and other serious bacterial infections—often raise RDW. Chronic infections such as tuberculosis, HIV, and parasitic diseases like malaria can also increase RDW. Inflammation, hemolysis and disrupted bone marrow erythropoiesis produce variable red cell sizes (anisocytosis), which shows as an elevated RDW and often signals more severe or chronic infectious processes.