What is the diagnosis and treatment for a 54-year-old female with microcytic anemia, indicated by a hemoglobin (Hb) level of 10.4, mean corpuscular volume (MCV) of 75, mean corpuscular hemoglobin (MCH) of 21.5, mean corpuscular hemoglobin concentration (MCHC) of 28.7, and red cell distribution width (RDW) of 21.9?

Diagnosis: Iron Deficiency Anemia

This 54-year-old woman has iron deficiency anemia (IDA), and she requires immediate gastrointestinal evaluation to exclude malignancy, as this is the most critical concern in post-menopausal women with IDA. 1

Diagnostic Confirmation

The laboratory findings definitively indicate microcytic, hypochromic anemia:

• Hemoglobin 10.4 g/dL (anemia by WHO criteria: <12.0 g/dL in non-pregnant women) 2
• MCV 75 fL (microcytosis: <80 fL) 3, 4
• MCH 21.5 pg (hypochromia, more reliable marker than MCV for iron deficiency) 2
• MCHC 28.7 g/dL (low, reflecting severe iron restriction during red blood cell production) 1, 5
• RDW 21.9% (markedly elevated, distinguishing IDA from thalassemia minor which typically has RDW <14%) 1, 5

Essential Next Steps for Diagnosis

You must obtain serum ferritin and C-reactive protein immediately to confirm iron deficiency and assess for concurrent inflammation. 1, 5

• Ferritin <15 μg/L is diagnostic of iron deficiency (specificity 0.99) 2
• Ferritin <45 μg/L warrants GI investigation even with inflammation (specificity 0.92) 2
• Ferritin >100 μg/L essentially excludes iron deficiency 1
• Transferrin saturation <30% supports the diagnosis 1

Mandatory Gastrointestinal Investigation

All post-menopausal women with iron deficiency require both upper endoscopy (with small bowel biopsy) and colonoscopy to exclude malignancy, even without overt bleeding. 1 This is non-negotiable because:

• Gastrointestinal blood loss is the predominant cause in post-menopausal women 1
• Excluding colonic and gastric carcinoma is the prime concern 1
• This applies regardless of anemia severity—mild anemia is equally indicative of important disease 1

Critical Pitfall to Avoid

Do not attribute this to dietary insufficiency without excluding GI malignancy. 1 The elevated RDW (21.9%) indicates true iron deficiency rather than thalassemia trait, which would show normal or low RDW. 1, 5

Treatment Algorithm

Step 1: Initiate Oral Iron Replacement

Start ferrous sulfate 324 mg (65 mg elemental iron) once daily on an empty stomach. 6

• Continue until hemoglobin normalizes AND iron stores are fully replenished (typically 3-6 months total) 3, 7
• Take 2 hours away from tetracycline antibiotics if applicable 6
• Common side effects include GI discomfort, nausea, constipation, or diarrhea 6

Step 2: Consider Intravenous Iron If:

• Oral iron is not tolerated due to GI side effects 2
• Malabsorption is documented 3
• Hemoglobin fails to rise by 1-2 g/dL after 4-6 weeks of adequate oral therapy 2
• Patient requires rapid correction 2

Step 3: Monitor Response

Recheck complete blood count in 4-6 weeks:

• Expected hemoglobin rise: 1-2 g/dL if treatment is effective 3, 7
• Reticulocyte count should increase within 7-10 days 3
• Continue iron supplementation for 3-6 months after hemoglobin normalizes to replenish stores 3, 7

Differential Diagnosis Considerations

While IDA is most likely given the elevated RDW, briefly consider:

• Thalassemia minor: Excluded by markedly elevated RDW (21.9% vs. expected <14%) 1, 5
• Anemia of chronic disease: Less likely to cause MCHC this low; ferritin and CRP will clarify 1, 5
• Combined deficiencies: Iron plus folate/B12 deficiency can mask microcytosis but show elevated RDW (as seen here) 1

Long-Term Outlook

Treatment of the underlying cause cures the anemia. 1 Even if no GI source is identified after thorough investigation, the long-term prognosis remains good with iron supplementation. 1