What is the diagnosis and treatment for a patient with mild anemia and elevated RDW?

Microcytic Anemia with Elevated RDW: Iron Deficiency Until Proven Otherwise

This patient has mild microcytic anemia (Hgb 11.4 g/dL, MCH 25.4, MCHC 28.7) with elevated RDW (16.4%), which strongly suggests iron deficiency anemia and requires immediate evaluation with serum ferritin, followed by investigation for gastrointestinal blood loss in adults. 1

Laboratory Interpretation

The combination of findings points to a specific diagnosis:

• Hemoglobin 11.4 g/dL qualifies as mild anemia (defined as Hgb ≤11.9 and ≥10 g/dL) 1
• Low MCH (25.4) and MCHC (28.7) indicate microcytic, hypochromic red cells characteristic of iron deficiency 1
• Elevated RDW (16.4%) reflects anisocytosis and is highly sensitive for iron deficiency anemia, with studies showing mean RDW of 18.2 ± 3.8 in IDA patients versus 13.2 ± 1.1 in controls 2, 3
• The elevated RDW distinguishes iron deficiency from other microcytic anemias like thalassemia trait (where RDW typically remains normal at 15.1 ± 1.2) 2

A common pitfall: elevated RDW can also occur with combined deficiencies (e.g., folate plus iron) or chronic disease, but the microcytic indices make iron deficiency the primary concern 1

Diagnostic Workup Algorithm

Step 1: Confirm Iron Deficiency

• Serum ferritin is the most powerful test for iron deficiency 1
  • Ferritin <12 μg/dL is diagnostic of iron deficiency 1
  • Ferritin 12-100 μg/dL suggests iron deficiency if no inflammation present 1
  • Ferritin >100 μg/dL essentially excludes isolated iron deficiency 1
• Obtain complete iron panel: transferrin saturation (TfS <30% supports diagnosis), serum iron 1
• Check reticulocyte count to assess bone marrow response 1

Step 2: Identify the Underlying Cause

• Detailed medication history, particularly NSAID use (common cause of occult GI bleeding) 1
• Dietary assessment for inadequate iron intake, though borderline deficient diets should not preclude full investigation 1
• Assess for blood loss: stool for occult blood, menstrual history in premenopausal women 1
• Peripheral blood smear to exclude other causes 1

Step 3: Gastrointestinal Investigation (Critical in Adults)

• In adult men and postmenopausal women with confirmed iron deficiency, GI blood loss is the most common cause and requires investigation for malignancy 1
• Both upper endoscopy with small bowel biopsy AND colonoscopy (or barium enema) are recommended to exclude gastric cancer, colon cancer/polyps, celiac disease, and angiodysplasia 1
• This applies even with mild anemia, as severity does not predict presence of serious pathology 1

Step 4: Additional Testing if Indicated

• Vitamin B12 and folate levels if macrocytosis develops or combined deficiency suspected 1
• Renal function assessment (chronic kidney disease causes normocytic anemia but can coexist) 1
• C-reactive protein to assess for chronic inflammation 1

Treatment Approach

Oral Iron Replacement

• Initiate oral iron therapy once iron deficiency is confirmed 1, 4
• Standard dosing: 100-200 mg elemental iron daily, though lower-dose formulations may be equally effective with fewer adverse effects 4
• Expect hemoglobin normalization by 8 weeks in most patients 4
• Monitor response with repeat CBC at 3-4 weeks (expect Hgb increase ≥2 g/dL) 1
• RDW and red cell morphology improve significantly after iron therapy 3

When Oral Iron Fails

• Consider parenteral iron infusion for patients who cannot tolerate or do not respond to oral therapy 4
• Non-response suggests incorrect diagnosis, ongoing blood loss, malabsorption, or chronic inflammation 1

Transfusion Rarely Needed

• Reserved for symptomatic patients with Hgb ≤7-8 g/dL or hemodynamic instability 1
• If transfusion required, follow with intravenous iron supplementation 1

Critical Pitfalls to Avoid

• Do not attribute iron deficiency to diet alone without excluding GI pathology in adults—asymptomatic colon and gastric cancers commonly present with iron deficiency anemia 1
• Stop NSAIDs whenever possible as they are a common reversible cause 1
• Do not assume thalassemia trait based on ethnicity alone—confirm with hemoglobin electrophoresis if RDW is normal despite microcytosis 1
• In patients with chronic inflammation (ferritin 30-100 μg/dL, TfS <20%), consider combined iron deficiency and anemia of chronic disease 1
• Ensure iron stores are normalized before declaring a patient pyridoxine-refractory in rare genetic causes 1

The elevated RDW in this case correlates inversely with hemoglobin level and transferrin saturation, reflecting the severity of iron deficiency 2. Treatment of the underlying cause will cure the anemia, and even when no cause is detected, long-term prognosis is good 1.