What does an elevated Red Cell Distribution Width (RDW) mean on a Complete Blood Count (CBC)?

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Dainyal Siddiqui, MD

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Manuel Jimenez, MD

Cardiology

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Franz Pierre-Louis, MD

Infectious Disease

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Last updated: April 4, 2025 • View editorial policy

From the Guidelines

An elevated Red Cell Distribution Width (RDW) on a Complete Blood Count (CBC) is a strong indicator of iron deficiency anemia, and it is essential to investigate further to determine the underlying cause, as suggested by the European Consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases 1. Elevated RDW values typically range from above 14.5%, with higher values suggesting greater size variability among red blood cells, a condition called anisocytosis. This finding often serves as an early indicator of various health conditions including iron deficiency anemia, vitamin B12 or folate deficiency, hemolytic anemia, certain inflammatory conditions, or liver disease. Some key points to consider when evaluating an elevated RDW include:

  • The RDW becomes elevated when your body produces new red blood cells of different sizes alongside existing ones, or when red blood cells are being destroyed at an abnormal rate.
  • Iron deficiency anemia is a common cause of elevated RDW, and it is essential to investigate further to determine the underlying cause, as suggested by the third European evidence-based consensus on diagnosis and management of ulcerative colitis 2.
  • Other potential causes of elevated RDW include vitamin B12 or folate deficiency, hemolytic anemia, and certain inflammatory conditions.
  • If you receive a CBC result with an elevated RDW, it's crucial to follow up with your healthcare provider for further evaluation, as this finding alone isn't diagnostic of a specific condition but rather suggests the need for additional testing to determine the underlying cause.
  • Your doctor may order tests like iron studies, vitamin B12 levels, or other specific blood tests based on your symptoms and medical history, as recommended by the European Consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases 1.

From the Research

Elevated RDW on CBC

Elevated RDW (Red Cell Distribution Width) on a Complete Blood Count (CBC) test can indicate a variation in the size of red blood cells.

  • This variation can be caused by several factors, including iron deficiency anemia, vitamin B12 or folate deficiency, and other conditions that affect red blood cell production 3, 4.
  • A study published in the International Journal of Laboratory Hematology found that treatment of iron deficiency anemia with pharmacological iron increased serum folate and vitamin B12 levels in young adult women, suggesting a relationship between iron deficiency and vitamin B12 and folate levels 4.
  • However, the provided studies do not directly address the meaning of elevated RDW on CBC, but rather discuss the relationship between iron deficiency, vitamin B12, and folate levels.
  • Other studies, not included in the provided evidence, would be necessary to fully understand the implications of elevated RDW on CBC.
  • The studies provided do not offer a direct explanation for elevated RDW, but they do discuss the importance of iron, vitamin B12, and folate in the production of red blood cells, which could be related to RDW 3, 4.

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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