Elevated RDW with Normal Red Cell Indices
Your markedly elevated RDW of 42.8 (normal range typically 11.5-14.5%) with otherwise normal MCV, MCH, and MCHC most likely indicates early iron deficiency or a mixed anemia picture where microcytic and macrocytic processes are neutralizing each other. 1
What These Values Mean
Your red blood cell indices show:
- MCV 91.9 fL (normal): Average red blood cell size is normal
- MCH 33.4 pg (normal): Average hemoglobin content per cell is normal
- MCHC 36.4 g/dL (normal): Hemoglobin concentration is normal
- RDW 42.8% (markedly elevated): Extreme variation in red blood cell sizes
- MPV 8.8 fL (normal): Platelet size is normal
Clinical Significance of Elevated RDW
The dramatically elevated RDW indicates significant anisocytosis (variation in red blood cell sizes), which is a sensitive indicator of iron deficiency even before MCV becomes abnormal. 1 This pattern suggests:
- Early iron deficiency anemia is the most common cause, where RDW rises before MCV drops 1, 2
- Mixed deficiency states where both microcytic (iron deficiency) and macrocytic (B12/folate deficiency) processes coexist, neutralizing each other to produce normal MCV but markedly elevated RDW 1
- Chronic inflammation or chronic disease can produce this pattern, particularly in inflammatory bowel disease 1
Recommended Diagnostic Workup
You need immediate iron studies and inflammatory markers to determine the cause: 1
- Serum ferritin: <30 μg/L indicates iron deficiency in the absence of inflammation; up to 100 μg/L may still indicate iron deficiency if inflammation is present 1
- Transferrin saturation (TSAT): <20% suggests iron deficiency 1
- C-reactive protein (CRP): Helps interpret ferritin levels, as ferritin is an acute phase reactant 1
- Complete blood count with hemoglobin: To assess for anemia (Hgb <12 g/dL in women, <13 g/dL in men) 1
- Reticulocyte count: Low/normal suggests deficiency states; elevated suggests hemolysis or blood loss 1
If iron studies are normal or equivocal, add: 1
- Vitamin B12 and folate levels: To exclude combined deficiency causing the mixed picture 1
- Peripheral blood smear: To visualize red blood cell morphology directly 1
Common Pitfalls to Avoid
Do not assume normal MCV rules out iron deficiency. 1 RDW elevation is often the earliest laboratory indicator of iron deficiency, appearing before MCV decreases. 2, 3
Do not ignore the possibility of coexisting deficiencies. 1 When microcytosis and macrocytosis coexist (such as combined iron and B12/folate deficiency), they neutralize each other resulting in normal MCV, but RDW remains markedly elevated due to the mixed population of small and large red blood cells. 1
In the presence of inflammation (elevated CRP), ferritin levels up to 100 μg/L may still represent iron deficiency. 1 Ferritin is an acute phase reactant and can be falsely elevated by inflammation, masking true iron deficiency.
Next Steps Based on Results
If ferritin <30 μg/L (or <100 μg/L with inflammation) and TSAT <20%: 1
- Diagnose iron deficiency anemia
- Investigate source of iron loss (gastrointestinal blood loss most common in adults)
- Consider stool guaiac testing for occult blood 1
- Initiate iron supplementation 1
If ferritin >100 μg/L and TSAT <20%: 1
- Diagnose anemia of chronic disease
- Investigate underlying inflammatory condition
- Consider functional iron deficiency
If ferritin 30-100 μg/L: 1
- Likely combination of iron deficiency and chronic disease
- Treat both the underlying inflammation and provide iron supplementation
If all iron studies are normal: 1
- Measure B12 and folate levels
- Consider hematology referral if cause remains unclear after extended workup