Microcytic Anemia with Thrombocytosis: Iron Deficiency Anemia
This patient has iron deficiency anemia (IDA) based on the microcytic hypochromic pattern (Hgb 11.1, MCV 76.5, MCH 23.5, MCHC 30.7), and the thrombocytosis (PLT 469) is a reactive phenomenon commonly seen in IDA. 1, 2
Diagnostic Interpretation
The laboratory findings strongly indicate iron deficiency anemia:
- Hemoglobin 11.1 g/dL is below normal range, confirming anemia 1
- MCV 76.5 fL indicates microcytosis (reference range 79-97 fL) 1
- MCH 23.5 pg and MCHC 30.7 g/dL both indicate hypochromia, characteristic of iron deficiency 1
- Thrombocytosis (PLT 469) is a common reactive finding in iron deficiency anemia, not thrombocytopenia 3
The combination of low MCV, low MCH, and low MCHC strongly suggests iron deficiency anemia as the primary diagnosis. 1, 2
Required Confirmatory Testing
Order serum ferritin, serum iron, total iron binding capacity (TIBC), and transferrin saturation immediately to confirm iron deficiency. 1, 2
Diagnostic Thresholds:
- Serum ferritin <12 μg/dL is diagnostic of iron deficiency 2, 4
- Ferritin 12-100 μg/dL may still indicate iron deficiency if inflammation is present 2, 4
- Ferritin >100 μg/dL essentially excludes iron deficiency 2, 4
- Transferrin saturation <30% supports iron deficiency diagnosis 2, 4
If ferritin is between 30-100 μg/L with evidence of inflammation, consider combined iron deficiency and anemia of chronic disease. 5
Investigate the Underlying Cause
In all patients with confirmed iron deficiency, identify the source of iron loss—this is mandatory, especially in men and non-menstruating women. 1, 4
Common causes include:
- Gastrointestinal blood loss (most common in men and postmenopausal women, including NSAID-induced bleeding) 4
- Menstrual blood loss (most common in premenopausal women) 3
- Dietary insufficiency (less common in developed countries) 4
- Malabsorption disorders (celiac disease, inflammatory bowel disease) 4
Treatment Approach
Initiate oral iron supplementation as first-line therapy: ferrous sulfate 325 mg (65 mg elemental iron) 1-3 times daily. 1
Optimization strategies:
- Take on an empty stomach with vitamin C to enhance absorption 1
- Monitor for gastrointestinal side effects (nausea, constipation, dark stools) and reassess compliance if no response after 4-8 weeks 1
- Expected response: Hemoglobin should rise ≥10 g/L within 2 weeks if iron deficiency is the correct diagnosis 2
When to use intravenous iron:
- Malabsorption documented 6
- True intolerance to oral iron (not just minor GI upset) 7
- Iron losses exceeding maximal oral replacement capacity 7
- Pregnancy or heart failure with iron deficiency (special considerations required) 6
Thrombocytosis Management
The thrombocytosis requires no specific treatment—it will resolve spontaneously once iron deficiency is corrected. 3
Thrombocytosis is a reactive phenomenon in iron deficiency anemia, with platelet counts typically normalizing 2 months after iron repletion. 3 Do not initiate antiplatelet therapy or anticoagulation based solely on this reactive thrombocytosis.
Important Pitfalls to Avoid
- Do not assume dietary insufficiency or ethnic background explains microcytosis without laboratory confirmation—thalassemia must be excluded with hemoglobin electrophoresis if iron studies are normal or if MCV is extremely low with elevated red cell count 2, 4
- Do not overlook genetic disorders if anemia is refractory to iron supplementation after 4-8 weeks—consider iron-refractory iron-deficiency anemia (IRIDA) or other rare causes 4
- In the presence of inflammation (elevated CRP, active IBD, malignancy), ferritin up to 100 μg/L may still represent iron deficiency 5
- Replete iron stores completely, not just correct the hemoglobin—continue iron therapy for 3-6 months after hemoglobin normalizes 7