What is the appropriate work‑up and treatment for a 50‑year‑old woman with a platelet count of 471 ×10⁹/L, hemoglobin 10.3 g/dL, hematocrit 32.8%, MCH 25.8 pg, and ferritin 4 ng/mL?

Reactive Thrombocytosis Secondary to Severe Iron Deficiency Anemia

This patient has severe iron deficiency anemia (ferritin 4 ng/mL) causing reactive thrombocytosis (platelet count 471), and the primary treatment is aggressive iron replacement—the platelet count will normalize as the anemia corrects.

Clinical Interpretation

The laboratory findings reveal:

• Severe iron deficiency: Ferritin 4 ng/mL (well below the 45 ng/mL threshold for diagnosing iron deficiency) 1
• Microcytic anemia: Hemoglobin 10.3 g/dL, hematocrit 32.8%, MCH 25.8 pg (all indicating microcytic hypochromic anemia)
• Reactive thrombocytosis: Platelet count 471 × 10⁹/L

This constellation is classic for reactive thrombocytosis secondary to iron deficiency anemia 2. The elevated platelet count will decrease by approximately 16-27 × 10⁹/L following iron replacement 3. This is NOT a primary myeloproliferative disorder given the severe iron deficiency and only modest thrombocytosis.

Immediate Work-Up Required

Rule Out Gastrointestinal Blood Loss (Priority #1)

At age 50, this postmenopausal woman requires gastrointestinal evaluation to identify the source of iron loss 1, 4:

• Upper endoscopy and colonoscopy are indicated for any degree of anemia with iron deficiency in this age group 4
• Look specifically for: occult malignancy, celiac disease, H. pylori infection, angioectasias, inflammatory bowel disease
• Do NOT delay investigation waiting for iron replacement response—proceed with endoscopic evaluation promptly 4

Additional Baseline Testing

• Celiac serology (tissue transglutaminase antibodies)
• H. pylori testing (stool antigen or breath test)
• Menstrual history (though at age 50, likely perimenopausal/postmenopausal)
• Dietary assessment for inadequate iron intake
• Stool for occult blood (though negative results don't exclude GI pathology)

Myeloproliferative Disorder Exclusion

Given the modest thrombocytosis (471 vs. extreme thrombocytosis ≥1000 × 10⁹/L) and clear iron deficiency, JAK2 mutation testing is NOT immediately necessary 2, 5. The thrombocytosis is reactive. However, if platelet count fails to normalize after complete iron repletion, then consider JAK2V617F, CALR, and MPL mutation testing 5.

Treatment Algorithm

Step 1: Initiate Iron Replacement Immediately

Oral iron is first-line unless contraindications exist 1:

• Ferrous sulfate 325 mg (65 mg elemental iron) once daily on an empty stomach
• If not tolerated, try with meals or switch to ferrous fumarate or ferrous gluconate
• Add vitamin C 500 mg with each dose to enhance absorption 1
• Expect hemoglobin rise ≥10 g/L within 2 weeks if compliant 4

Consider intravenous iron if:

• Severe symptoms requiring rapid correction
• Oral iron intolerance (nausea, constipation, abdominal pain)
• Malabsorption suspected (celiac disease, inflammatory bowel disease)
• Need for rapid correction before planned surgery
• Failure to respond to oral iron after 4-6 weeks 1

Step 2: Monitor Response

Recheck complete blood count in 2 weeks:

• Hemoglobin should increase ≥10 g/L 4
• Platelet count should begin declining 3
• Reticulocyte count should increase (indicates bone marrow response)

Recheck at 4-6 weeks:

• Continue monitoring hemoglobin and platelet trends
• Check ferritin once hemoglobin normalizes

Target ferritin >45 ng/mL for adequate iron stores 1, though some evidence suggests 30-40 ng/mL may be sufficient for erythropoiesis 6.

Step 3: Continue Iron Until Stores Replete

• Continue iron supplementation for 3-6 months after hemoglobin normalizes to replenish iron stores
• Target ferritin >45 ng/mL 1
• The platelet count will normalize as iron stores improve 2, 3

Aspirin Consideration

Do NOT routinely start aspirin for this degree of thrombocytosis in the setting of iron deficiency:

• Platelet count 471 is only mildly elevated
• This is reactive, not clonal thrombocytosis
• Risk of bleeding may actually be increased with iron deficiency despite elevated platelet count 3
• Aspirin is reserved for essential thrombocythemia (platelet count typically >600-1000 with JAK2/CALR/MPL mutations) 5

Common Pitfalls to Avoid

1. Assuming thrombocytosis is primary: Always check ferritin before pursuing myeloproliferative workup in patients with modest thrombocytosis
2. Delaying GI evaluation: Age 50 with iron deficiency anemia mandates endoscopic evaluation regardless of iron replacement response 4
3. Stopping iron too early: Continue for 3-6 months after hemoglobin normalizes to replenish stores
4. Starting aspirin unnecessarily: This increases bleeding risk without benefit in reactive thrombocytosis
5. Missing celiac disease: Common cause of iron malabsorption requiring specific management 1

Expected Outcomes

With appropriate iron replacement:

• Hemoglobin should normalize within 2-3 months
• Platelet count will decrease by 16-27 × 10⁹/L and normalize within 2-4 months 3
• Symptoms (fatigue, weakness) will improve significantly
• Quality of life will be restored 1

If platelet count remains elevated (>450 × 10⁹/L) after complete iron repletion (ferritin >45 ng/mL, hemoglobin normalized for 3+ months), then pursue JAK2/CALR/MPL mutation testing to evaluate for essential thrombocythemia 5.