Microcytic Hypochromic Anemia with High RBC Count and High RDW
Primary Diagnosis
The most likely diagnosis is iron deficiency anemia (IDA), which requires immediate investigation for the source of iron loss, particularly gastrointestinal bleeding in adults. 1, 2, 3
The laboratory pattern you describe—high RBC count with low hemoglobin, low MCV, low MCH, and high RDW—creates a distinctive signature that strongly points toward iron deficiency rather than other causes of microcytic anemia. 2, 3
Why This Pattern Indicates Iron Deficiency
High RDW (>14%) combined with low MCV is the key discriminator: This combination has 91.4% accuracy in distinguishing iron deficiency from thalassemia trait, which typically shows normal or only mildly elevated RDW despite microcytosis. 3, 4
The elevated RBC count with microcytosis reflects the bone marrow's compensatory attempt to maintain oxygen-carrying capacity by producing more cells, even though each cell is smaller and contains less hemoglobin. 2
High RDW appears early in iron deficiency, often before MCV drops significantly, reflecting the mixed population of older normal-sized cells and newer microcytic cells. 2, 3
Essential Diagnostic Workup
Confirm iron deficiency with serum ferritin as the most powerful single test:
- Ferritin <30 μg/L (in absence of inflammation) is diagnostic of iron deficiency 1, 2, 3
- Ferritin <100 μg/L may still indicate iron deficiency when inflammation is present (check CRP concurrently) 1, 2, 3
- Ferritin >100 μg/L essentially excludes iron deficiency 1
Additional confirmatory tests:
- Transferrin saturation <30% supports iron deficiency 1, 2
- Reticulocyte count to assess bone marrow response 2, 3
- CRP to identify concurrent inflammation that may falsely elevate ferritin 2, 3
Critical Pitfall to Avoid
Serum ferritin can be falsely elevated in inflammatory conditions, chronic disease, malignancy, or liver disease, potentially masking true iron deficiency. 1, 2 In these situations, ferritin up to 100 μg/L may still be consistent with iron deficiency. 2
Mandatory Investigation for Cause
All adult patients with confirmed iron deficiency require gastrointestinal evaluation to identify the source of blood loss, as this may reveal serious pathology including malignancy. 1
Upper and lower GI endoscopy should be performed unless there is clear evidence of significant non-gastrointestinal blood loss (e.g., menorrhagia in premenopausal women). 1
Common GI causes to investigate include: 1
- Colon cancer/polyps
- NSAID-induced gastropathy
- Angiodysplasia
- Gastric cancer
- Celiac disease
- Inflammatory bowel disease
Treatment Approach
Oral iron supplementation is first-line treatment for most patients with iron deficiency anemia:
- Standard oral iron preparations are inexpensive and usually well-tolerated 5
- Continue treatment until iron stores are fully repleted, not just until hemoglobin normalizes 5
- Response to oral iron for 3 weeks can confirm the diagnosis if doubt remains 1
Parenteral iron (IV iron dextran) is indicated when: 5
- Malabsorption is present
- Losses exceed maximal oral replacement capacity
- True intolerance to oral iron occurs
- Rapid repletion is needed (e.g., heart failure, pregnancy) 6
Alternative Diagnoses to Consider
Thalassemia trait should be considered if:
- RDW is normal or only mildly elevated (≤14%) despite microcytosis 1, 3
- RBC count is disproportionately elevated (often >5.5 million/μL) 1
- Ferritin is normal or elevated 1
- Family history or ethnicity suggests hemoglobinopathy 1
- Hemoglobin electrophoresis is required for definitive diagnosis 1
Combined deficiency (iron plus folate/B12) may present with:
- Normal MCV (microcytosis masked by macrocytosis) but elevated RDW 1, 3
- This pattern requires checking both iron studies and vitamin levels 3
Anemia of chronic disease typically shows: