From the Guidelines
An elevated Red Cell Distribution Width (RDW) of 20.2% with otherwise normal CBC parameters warrants further investigation, as it indicates significant variation in red blood cell size (anisocytosis). This finding, even in isolation, should not be dismissed as it may be an early indicator of developing conditions before other CBC abnormalities appear. The most recent and highest quality study 1 suggests that a raised RDW may be recognized in combined deficiency, such as with folate deficiency, and may also be present in the anaemia of chronic disease due to the inability to use iron.
Key Considerations
- The RDW elevation occurs because the bone marrow is producing red cells of varying sizes in response to underlying conditions, often before changes in hemoglobin or MCV become apparent.
- Common causes of isolated RDW elevation include early iron deficiency, early B12 or folate deficiency, emerging hemoglobinopathies, liver disease, or certain medications.
- Serum ferritin concentration is the most powerful test for iron deficiency, as stated in 1 and 1, with a concentration of <12 μg/dl being diagnostic of iron deficiency.
Recommended Approach
- I recommend a clinical evaluation including a thorough history focusing on dietary habits, alcohol use, medication review, and symptoms of anemia or chronic disease.
- Follow-up testing should include iron studies (ferritin, iron, TIBC), vitamin B12, folate levels, reticulocyte count, and possibly hemoglobin electrophoresis.
- Repeat CBC in 4-8 weeks is also advisable to monitor for changes.
- Addressing the underlying cause is essential rather than treating the RDW value itself, as emphasized in 1 and 1.
From the Research
Significance of RDW in CBC
The Red Blood Cell Distribution Width (RDW) is a parameter in the Complete Blood Count (CBC) test that measures the variation in the size of red blood cells.
- An RDW of 20.2 is considered elevated, as the normal range is typically between 11.8 and 14.5% 2.
- Elevated RDW values can indicate a range of conditions, including iron deficiency anemia, vitamin B12 or folate deficiency, and other hematologic disorders 2.
- However, in isolation with all other parameters being normal, the clinical significance of an elevated RDW is not well established 3, 4.
Diagnostic Implications
- The RDW has unique diagnostic applications and prognostic implications that can be incorporated into clinical practice 2.
- It can be used as a marker to predict cardiovascular disease (CVD) and metabolic diseases, in combination with other CBC components 5.
- However, more research is needed to fully understand the significance of an isolated elevated RDW in the absence of other abnormalities 3, 4.
Clinical Considerations
- Clinicians should consider the patient's medical history, physical examination, and other laboratory results when interpreting an elevated RDW 3, 4.
- Further testing or consultation with a hematologist may be necessary to determine the underlying cause of the elevated RDW 3.
- The RDW should be considered in the context of the entire CBC result, rather than in isolation 2.