What is the most likely diagnosis and recommended management for a patient with a complete blood count showing low hemoglobin, low hematocrit, microcytosis, low mean corpuscular hemoglobin, high red cell distribution width, and thrombocytosis?

Laboratory Interpretation: Microcytic Hypochromic Anemia with Thrombocytosis

This patient has iron deficiency anemia (IDA), and you must confirm this with serum ferritin testing immediately, then investigate for the source of iron loss—particularly gastrointestinal pathology.

Key Laboratory Findings

The serial CBC results show a persistent pattern highly suggestive of IDA:

• Microcytosis: MCV 75-76 fL (consistently low)
• Hypochromia: MCH 24.3-24.6 pg (consistently low)
• Anemia: Hemoglobin 10.6-10.9 g/dL (persistently low)
• Elevated RDW: 16.7-18.1% (indicating heterogeneous red cell population)
• Reactive thrombocytosis: Platelets trending down from 522 to 406 (common in IDA)

Diagnostic Approach

Serum ferritin is the single most useful test to confirm iron deficiency 1. You need this result to proceed:

• Ferritin <15 μg/L: Highly specific for iron deficiency (99% specificity) 1
• Ferritin <30 μg/L: Generally indicates low body iron stores 1
• Ferritin <45 μg/L: Optimal cutoff balancing sensitivity and specificity (92% specificity) 1

Critical Caveat

Ferritin is an acute phase reactant and can be falsely normal in inflammatory conditions. If ferritin is 45-150 μg/L with clinical suspicion for IDA, consider additional testing (transferrin saturation, inflammatory markers) 1.

Why This is Iron Deficiency Anemia

The combination of low MCV + low MCH + elevated RDW has 94% sensitivity for iron deficiency 2. The MCH is particularly reliable as it's less affected by storage conditions and machine variability 1. The elevated RDW reflects the mixed population of older normocytic cells and newer microcytic cells as iron stores deplete 2.

The reactive thrombocytosis (initially 522) is a classic finding in IDA and typically resolves with iron repletion.

Differential Considerations to Exclude

While IDA is most likely, you must exclude:

Thalassemia Trait

• Key distinguishing feature: Thalassemia typically shows MCV disproportionately low relative to mild or absent anemia 1
• This patient has significant anemia (Hb 10.6 g/dL) with only moderate microcytosis (MCV 75-76 fL)
• If ferritin is normal: Order hemoglobin electrophoresis, particularly if patient has Mediterranean, African, or Southeast Asian ancestry 1

Anemia of Chronic Disease

• Can cause microcytosis but usually less pronounced 3
• Ferritin typically normal or elevated (>150 μg/L makes IDA unlikely even with inflammation) 1

Management Algorithm

Step 1: Confirm Diagnosis

• Order serum ferritin immediately 1
• If ferritin <45 μg/L → Confirmed IDA, proceed to Step 2
• If ferritin 45-150 μg/L → Add transferrin saturation; consider inflammatory markers
• If ferritin >150 μg/L → Consider alternative diagnoses

Step 2: Investigate Source of Iron Loss

Investigation should be considered at any level of anemia in the presence of iron deficiency 1. The British Society of Gastroenterology guidelines emphasize that patients with more severe anemia are more likely to have serious underlying GI pathology 1.

For this patient with Hb 10.6 g/dL:

• Men or non-menstruating women: Bidirectional GI investigation (upper and lower endoscopy) is warranted 1
• Menstruating women: Consider gynecologic causes first, but don't dismiss GI pathology
• NICE fast-track referral criteria: Hb <110 g/L in men or <100 g/L in non-menstruating women for suspected colorectal cancer 1—this patient meets criteria if male

Step 3: Initiate Iron Replacement

Start oral iron therapy while investigating:

• Diagnostic and therapeutic: A hemoglobin rise ≥10 g/L within 2 weeks strongly confirms absolute iron deficiency, even if iron studies are equivocal 1
• Standard oral iron preparations are first-line and inexpensive 4
• Reserve IV iron for malabsorption, intolerance, or inadequate response 4

Critical Pitfall to Avoid

Do not assume this is "just" iron deficiency without investigating the cause. The persistent nature of these findings over serial measurements suggests ongoing iron loss. Missing an underlying GI malignancy (particularly colorectal cancer in appropriate age groups) has significant mortality implications 1. The guidelines explicitly state that relying solely on Hb cutoffs will miss some cancers, especially in men 1.