What is the most likely diagnosis and appropriate management for an elderly patient with hypochromic microcytic anemia and an elevated Red Cell Distribution Width (RDW)?

Diagnosis and Management of Microcytic Hypochromic Anemia with Elevated RDW in an Elderly Patient

This elderly patient most likely has iron deficiency anemia, and you should immediately order serum ferritin and transferrin saturation, then initiate oral iron supplementation with ferrous sulfate 200 mg three times daily while simultaneously investigating for gastrointestinal blood loss, particularly colonic pathology given the patient's age. 1, 2

Why Iron Deficiency is the Leading Diagnosis

The combination of hypochromic microcytic anemia (MCH 23.3, MCHC 29.2) with a markedly elevated RDW of 25.5 is pathognomonic for iron deficiency anemia rather than thalassemia trait. 1, 2 A low MCV with RDW >14.0% strongly indicates iron deficiency, while thalassemia minor typically presents with RDW ≤14.0%. 1, 3 The RDW elevation reflects the heterogeneous red cell population that develops as iron stores become progressively depleted—older normocytic cells coexist with newer microcytic hypochromic cells. 4

While some research suggests RDW has limitations in distinguishing these conditions, 5 the markedly elevated RDW of 25.5 in this case (well above the 14.0% threshold) makes iron deficiency overwhelmingly more likely than thalassemia. 4

Immediate Diagnostic Workup

Order serum ferritin first—it is the single most powerful test for iron deficiency. 6, 1, 2

• Ferritin <30 μg/L indicates low body iron stores, though a cutoff of 45 μg/L provides optimal sensitivity and specificity in practice. 1, 2
• Ferritin <12 μg/L is diagnostic of iron deficiency. 6
• If ferritin is >100 μg/L, iron deficiency is almost certainly not present. 6

Critical caveat: In elderly patients with concurrent inflammation, malignancy, or hepatic disease, ferritin may be falsely elevated above 12-15 μg/L despite true iron deficiency. 6 In such cases, ferritin up to 100 μg/L may still be consistent with iron deficiency. 1

Add transferrin saturation (TSAT) to the workup—it is more sensitive than hemoglobin alone for detecting iron deficiency. 1, 2 TSAT <30% supports the diagnosis. 6

Mandatory Investigation for Source of Blood Loss

In elderly patients with confirmed iron deficiency anemia, gastrointestinal investigation is mandatory unless there is documented significant non-GI blood loss. 6 This is non-negotiable because:

• In the elderly, investigation of the colon is likely to be more productive than upper GI endoscopy. 6
• Common causes include colonic cancer/polyps, angiodysplasia, NSAID use, and gastric cancer. 6
• Upper GI endoscopy reveals a cause in 30-50% of patients, but dual pathology (lesions in both upper and lower GI tracts) occurs in 10-15% of cases. 6

Recommended Investigation Sequence:

1. Perform upper GI endoscopy with small bowel biopsies—2-3% of patients with iron deficiency anemia have celiac disease. 6
2. Unless upper endoscopy reveals carcinoma or celiac disease, all patients should undergo colonoscopy or double contrast barium enema. 6
3. Document NSAID use and stop whenever possible—this is a common cause of occult GI blood loss. 6

Treatment Algorithm

Start oral iron supplementation immediately with ferrous sulfate 200 mg (65 mg elemental iron) three times daily. 1, 2

• Add ascorbic acid (vitamin C) to enhance iron absorption. 2
• Alternative formulations include ferrous gluconate or ferrous fumarate if GI side effects are intolerable. 1, 2
• Continue treatment for at least three months after correction of anemia to replenish iron stores. 1, 2

Expected Response:

A good response is defined as hemoglobin rise ≥10 g/L (≥1 g/dL) within 2 weeks, which confirms iron deficiency. 1, 2 If the patient fails to respond within 2-4 weeks, consider:

• Non-compliance
• Ongoing blood loss
• Malabsorption (consider IV iron if present) 1
• Rare genetic disorders of iron metabolism (unlikely in elderly patients) 6, 1

Monitoring Protocol

Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year, then after a further year. 1, 2

• Provide additional oral iron if hemoglobin or MCV falls below normal. 1, 2
• Expect hemoglobin increase of at least 2 g/dL within 4 weeks of starting treatment. 1, 2

Critical Pitfalls to Avoid

Do not assume dietary deficiency is the sole cause even if dietary history is positive—a full GI investigation is still required. 6 Borderline deficient diets are common in elderly patients, but this should not deter investigation for occult malignancy. 6

Do not accept oesophagitis, erosions, or peptic ulcer as the definitive cause of iron deficiency until lower GI tract has been examined. 6 Dual pathology is too common to skip colonoscopy. 6

Do not overlook combined deficiencies—microcytosis may be absent in combined iron and folate deficiency, which can be recognized by the raised RDW. 6 However, this patient's markedly elevated RDW with clear microcytosis makes isolated iron deficiency most likely.