What is the significance of an isolated elevated Red Cell Distribution Width (RDW)?

From the Guidelines

An isolated elevated Red Cell Distribution Width (RDW) is a sensitive but non-specific indicator of hematologic abnormalities and requires further investigation to determine the underlying cause, with a focus on assessing for nutritional deficiencies, such as iron, vitamin B12, or folate deficiency, as well as other potential causes like early hemoglobinopathies, liver disease, or inflammatory conditions. When evaluating an isolated elevated RDW, it is essential to review the patient's complete blood count to check for anemia or other abnormalities. According to the European Consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases 1, a wide size range of the red cells, indicated by a high RDW, can help identify iron deficiency, especially in situations where microcytosis and macrocytosis co-exist. The diagnostic approach should include:

• Serum iron studies, ferritin, B12, and folate levels to assess for nutritional deficiencies
• Reticulocyte count to evaluate the bone marrow's response to anemia
• Transferrin saturation and CRP levels to differentiate between iron deficiency anemia and anemia of chronic disease, as recommended by the third European evidence-based consensus on diagnosis and management of ulcerative colitis 1
• Other potential tests, such as haptoglobin, lactate dehydrogenase, and bilirubin, to investigate hemolysis or other underlying conditions If nutritional deficiencies are identified, appropriate supplementation should be initiated, such as iron supplements (typically ferrous sulfate 325mg daily) for iron deficiency, vitamin B12 (1000mcg daily orally or monthly injections) for B12 deficiency, or folate (1mg daily) for folate deficiency. In the absence of other abnormalities and with mild RDW elevation, monitoring with repeat CBC in 3 months may be appropriate, as RDW is elevated early in developing anemias because the bone marrow begins producing cells of varying sizes before anemia becomes apparent.

From the Research

Isolated Elevated RDW

• An isolated elevated Red Cell Distribution Width (RDW) can be an indicator of iron deficiency anemia, even in the absence of other abnormal red blood cell indices 2
• A study found that RDW had a sensitivity of 82.3% and specificity of 97.4% in detecting iron deficiency, making it a useful parameter in the early detection of iron deficiency anemia 2
• Elevated RDW can be seen in the latent stage of iron deficiency, before other red blood cell indices such as MCV, MCH, and MCHC become abnormal 2

Causes of Isolated Elevated RDW

• Iron deficiency is a common cause of isolated elevated RDW, and can be due to various factors such as bleeding, impaired iron absorption, inadequate dietary iron intake, and pregnancy 3
• Other causes of elevated RDW include vitamin B12 and folate deficiency, although these are less common 4

Clinical Significance of Isolated Elevated RDW

• An isolated elevated RDW can be a useful indicator of iron deficiency anemia, and can help guide further testing and treatment 2
• Elevated RDW has been associated with increased risk of mortality and morbidity in certain patient populations, such as those with chronic kidney disease and heart failure 3
• However, more research is needed to fully understand the clinical significance of isolated elevated RDW and its relationship to iron deficiency anemia and other conditions 5