Diagnosis: Iron Deficiency Anemia
The most likely diagnosis is iron deficiency anemia (IDA), based on the combination of mild anemia (hemoglobin 11.8 g/dL), low MCH (26.0 pg), low MCHC (31.3 g/dL), and markedly elevated RDW (17.7%). 1
Key Diagnostic Features
The laboratory pattern strongly points toward iron deficiency:
Elevated RDW (17.7%) with low hemoglobin is highly indicative of iron deficiency anemia, as the elevated RDW (>14.0%) reflects increased variation in red cell size (anisocytosis) that characteristically develops as iron stores become depleted 1, 2
Low MCH (26.0 pg) and low MCHC (31.3 g/dL) indicate hypochromia, which occurs when red blood cells contain insufficient hemoglobin due to iron deficiency 1
The RDW elevation precedes the development of frank microcytosis in iron deficiency, making it an early and sensitive marker—RDW increases progressively from prelatent (13.2%) to latent (14.0%) to overt iron deficiency anemia (15.6%) 2
Essential Confirmatory Testing
Before initiating treatment, obtain these specific tests:
Serum ferritin: <30 μg/L confirms iron deficiency in the absence of inflammation; <100 μg/L may still indicate iron deficiency if inflammation is present 3, 4, 1
C-reactive protein (CRP): Necessary to assess for inflammation that could elevate ferritin and mask true iron deficiency 3, 4
Critical Investigation for Underlying Cause
All adult men and post-menopausal women with confirmed iron deficiency require both upper and lower endoscopy to exclude gastrointestinal malignancy, regardless of anemia severity 4, 1. Common causes include:
- Gastrointestinal blood loss: Colonic cancer/polyps, gastric cancer, NSAID use, angiodysplasia, inflammatory bowel disease 1
- Malabsorption: Particularly celiac disease 1
- Menstrual blood loss: Most common in pre-menopausal women 1
- Poor dietary iron intake 1
Treatment Approach
Once iron deficiency is confirmed:
- Initiate oral iron supplementation as first-line therapy 1
- A therapeutic response after three weeks of oral iron confirms the diagnosis 1
- Continue iron therapy for 3-6 months after hemoglobin normalization to replenish iron stores 1
- If no response after 4 weeks, reassess diagnosis and adherence 1
- Consider intravenous iron if malabsorption or oral intolerance exists 1
Important Caveats
Do not empirically treat with iron without confirming iron deficiency through ferritin testing, as this approach could cause iron overload if the patient has thalassemia trait (though less likely given the elevated RDW) 4.
Consider combined deficiencies (iron plus B12 or folate), which can result in normal MCV despite iron deficiency and may complicate the laboratory picture 3, 4, 1.
Anemia of chronic disease can coexist with iron deficiency, particularly in inflammatory bowel disease patients, where functional iron deficiency occurs despite adequate iron stores 3, 1.