What are the potential causes and next steps for an elderly patient in their late 80s with a recent decline in complete blood count (CBC) results, including anemia (low red blood cell count, hemoglobin, and hematocrit), microcytosis (low mean corpuscular volume (MCV)), and hypochromia (low mean corpuscular hemoglobin (MCH)), after having normal CBC results four months prior?

Microcytic Hypochromic Anemia in an Elderly Patient: Diagnostic Approach

In an elderly patient with newly developed microcytic hypochromic anemia (low MCV and MCH), iron deficiency anemia from gastrointestinal blood loss is the most likely diagnosis and requires immediate investigation with serum ferritin, followed by upper endoscopy and colonoscopy to identify the bleeding source. 1, 2

Primary Differential Diagnosis

The combination of low RBC count, hemoglobin, hematocrit, MCV, and MCH defines microcytic hypochromic anemia. In an elderly patient with previously normal CBC, the key causes to consider are:

• Iron deficiency anemia - Most common cause, accounting for the majority of microcytic anemia cases 3, 4
• Anemia of chronic disease - Can present with microcytosis, though typically less pronounced 1, 4
• Thalassemia trait - Less likely given the recent onset and previously normal CBC 4
• Gastrointestinal malignancy - Critical consideration in elderly patients with new-onset iron deficiency 1, 2

Essential Initial Laboratory Testing

Order these tests immediately to establish the diagnosis:

• Serum ferritin - The single most powerful diagnostic test; <15 μg/L is diagnostic of iron deficiency, <30 μg/L indicates depleted stores 5, 2
• Iron studies - Including serum iron, total iron-binding capacity (TIBC), and transferrin saturation; expect low iron, high TIBC, and transferrin saturation <15-16% in iron deficiency 1, 5
• Red cell distribution width (RDW) - Elevated (>14%) supports iron deficiency over thalassemia trait 5, 2
• Reticulocyte count - Helps determine if bone marrow is responding appropriately 6

Critical Interpretation Pitfalls

• Ferritin is an acute phase reactant and can be falsely normal or elevated during inflammation, infection, or malignancy despite true iron deficiency 5, 2
• In the presence of inflammation, ferritin up to 100 μg/L may still indicate iron deficiency, but ferritin >150 μg/L essentially excludes absolute iron deficiency even with concurrent inflammation 5
• Combined deficiencies (iron plus B12/folate) can occur; check vitamin B12 and folate levels if RDW is markedly elevated 2

Mandatory Investigation for Blood Loss Source

In elderly patients, iron deficiency anemia is presumed to be caused by gastrointestinal blood loss until proven otherwise. 1, 2, 4

Gastrointestinal Evaluation Protocol

• Upper endoscopy first - Reveals a cause in 30-50% of patients 2
• Obtain small bowel biopsies during upper endoscopy to screen for celiac disease, present in 2-3% of iron deficiency anemia patients 1, 2
• Colonoscopy - Particularly important in patients over 50 years old 2
• Do NOT perform fecal occult blood testing - It is insensitive and non-specific and should not be used 1

When to Consider Further Small Bowel Evaluation

Further small bowel visualization is generally not necessary unless: 1

• The anemia is transfusion-dependent
• There has been visible blood loss (melena)
• Standard upper and lower endoscopy are unrevealing and anemia persists despite treatment

Treatment Approach

Start oral iron replacement immediately without waiting for confirmatory tests if the clinical picture is clear. 2

Iron Supplementation Protocol

• Ferrous sulfate 200 mg (65 mg elemental iron) three times daily - Most cost-effective first-line treatment 1, 2
• Alternative formulations (ferrous gluconate, ferrous fumarate) are equally effective if ferrous sulfate is not tolerated 1
• Add ascorbic acid (vitamin C) to enhance iron absorption, especially if response is poor 1
• Continue treatment for at least 3 months after anemia correction to replenish iron stores 1, 2

Expected Response

• Hemoglobin should rise by approximately 2 g/dL after 3-4 weeks of treatment 1
• Failure to respond suggests poor compliance, misdiagnosis, continued blood loss, or malabsorption 1

Monitoring Strategy

• Follow hemoglobin and red cell indices at 3-monthly intervals for one year, then after a further year 1, 2
• Provide additional oral iron if hemoglobin or MCV falls below normal 1
• Check ferritin in doubtful cases 1
• Further investigation is only necessary if hemoglobin and MCV cannot be maintained with iron supplementation 1

Special Considerations in Elderly Patients

The appropriateness of investigating patients with severe co-morbidity or advanced age should be carefully considered and discussed with patients and caregivers, especially if results would not influence management. 1

However, given the 4-month timeframe of decline and the high risk of gastrointestinal malignancy in elderly patients with new-onset iron deficiency, investigation is generally warranted unless significant co-morbidities preclude intervention. 1, 2

Additional Causes to Exclude

• Medication review - NSAIDs can cause gastrointestinal bleeding and should be stopped if possible 1
• Urinary tract bleeding - Check for hematuria, as urinary tract tumors may rarely present with iron deficiency anemia 1
• Chronic kidney disease - Check renal function, though this typically causes normocytic anemia 1, 6