What does an elevated Red Blood Cell (RBC) Distribution Width (RDW) of 14.6 indicate?

What Does an RDW of 14.6% Indicate?

An RDW of 14.6% is mildly elevated (normal ≤14.0%) and warrants further evaluation with complete blood count indices, serum ferritin, transferrin saturation, and CRP to identify the underlying cause, most commonly iron deficiency, early nutritional deficiencies, or inflammatory conditions. 1, 2

Understanding Your Result

• Your RDW of 14.6% exceeds the normal threshold of 14.0%, which represents the 95th percentile in reference populations 1
• This elevation indicates increased variation in red blood cell size (anisocytosis), suggesting heterogeneous erythrocyte populations 1
• The elevation is mild, falling in the 14.0-14.9% range, which is the lowest category of abnormal values 3

Immediate Diagnostic Workup Required

You need the following tests to determine the cause: 1, 2

• Complete blood count with MCV (mean corpuscular volume) - this is the critical next step
• Serum ferritin (<30 μg/L suggests iron deficiency; <100 μg/L if inflammation present)
• Transferrin saturation
• CRP (C-reactive protein to assess for inflammation)
• Reticulocyte count

Interpretation Based on MCV Pattern

If Your MCV is Low (Microcytic Anemia)

• High RDW + Low MCV strongly suggests iron deficiency anemia 1, 2
• This combination has high diagnostic accuracy for iron deficiency 2
• You will need investigation for sources of blood loss, particularly gastrointestinal 2

If Your MCV is Normal (Normocytic)

• High RDW + Normal MCV suggests early iron deficiency, vitamin B12/folate deficiency, or hemolysis 1
• This pattern occurs when microcytosis and macrocytosis coexist, canceling each other out 1
• Combined deficiencies (iron plus B12) can produce this pattern 2

If Your MCV is High (Macrocytic)

• Consider vitamin B12 or folate deficiency 1
• Hemolysis should be evaluated with reticulocyte count 1

Common Causes at This Level

• Iron deficiency - most common cause of elevated RDW with microcytosis 1, 2
• Early nutritional deficiencies - vitamin B12 or folate deficiency before MCV changes 1
• Inflammatory conditions - chronic inflammation causes elevated RDW through erythrocyte membrane injury 1
• Mixed deficiency states - simultaneous iron and vitamin deficiencies 2

Prognostic Implications

While your primary concern should be identifying the cause, elevated RDW carries prognostic significance:

• Higher RDW values correlate with increased mortality risk in hospitalized patients, though your mild elevation (14.6%) carries less risk than values ≥15.0% 3
• RDW reflects underlying metabolic derangements including oxidative stress, inflammation, and impaired erythropoiesis 4
• In elderly hospitalized patients, RDW 14.0-14.9% showed 2.7% mortality versus 12.2% for RDW ≥18.0% 3

Critical Pitfalls to Avoid

• Do not assume thalassemia trait based on ethnicity without laboratory confirmation - nearly half of thalassemia cases also show elevated RDW 5, 2
• Do not overlook gastrointestinal malignancy - if iron deficiency is confirmed in adult men or post-menopausal women, both upper and lower endoscopy are mandatory 2
• Do not attribute findings solely to inflammation - even with elevated CRP, investigate for concurrent iron or vitamin deficiencies 1
• Do not ignore combined deficiencies - check both iron studies and vitamin levels, as mixed deficiencies can mask each other 2

Next Steps Algorithm

1. Obtain MCV from your complete blood count 1, 2
2. Check serum ferritin and transferrin saturation 1, 2
3. If ferritin <30 μg/L (or <100 μg/L with inflammation): Diagnose iron deficiency and investigate blood loss sources 2
4. If ferritin normal but MCV normal/high: Check vitamin B12 and folate levels 1
5. If all nutritional markers normal: Evaluate for hemolysis (reticulocyte count, haptoglobin, LDH) and chronic inflammatory conditions 1