What is the interpretation and management for hypochromia, anisocytosis, and thrombocytosis?

Interpretation and Management of Hypochromia, Anisocytosis, and Thrombocytosis

The CBC findings of low MCHC (30.4 g/dL), elevated RDW (16.2%), and elevated platelets (453 x10³/uL) most likely represent iron deficiency anemia with reactive thrombocytosis, requiring iron supplementation and investigation of the underlying cause.

Understanding the CBC Abnormalities

Hypochromia (Low MCHC)

• MCHC (Mean Corpuscular Hemoglobin Concentration) of 30.4 g/dL (below normal range of 31.5-35.7 g/dL) indicates hypochromia, which is a reduction in hemoglobin concentration within red blood cells 1
• Hypochromia is a classic feature of iron deficiency anemia but can also occur in thalassemia and anemia of chronic disease 1
• MCH is considered a more reliable marker of iron deficiency than MCV as it is less dependent on storage and counting machines 1

Anisocytosis (Elevated RDW)

• RDW of 16.2% (above normal range of 11.7-15.4%) indicates significant variation in red cell size 1
• An elevated RDW is a sensitive indicator of iron deficiency, even when MCV may be normal 1, 2
• High RDW helps distinguish iron deficiency from thalassemia trait, as thalassemia typically shows more uniform microcytosis 3

Thrombocytosis

• Platelet count of 453 x10³/uL (above normal range of 150-450 x10³/uL) represents mild thrombocytosis 1
• Reactive thrombocytosis commonly occurs in iron deficiency anemia and inflammatory conditions 1

Diagnostic Approach

Initial Workup

• Complete iron studies should be performed, including serum ferritin, transferrin saturation (TSAT), and total iron-binding capacity 1
• Serum ferritin <15 μg/L is highly specific for iron deficiency (specificity 0.99) 1
• In the presence of inflammation, ferritin may be falsely normal; a cut-off of 45 μg/L provides better sensitivity while maintaining specificity of 0.92 1

Additional Testing

• Reticulocyte count to assess bone marrow response to anemia 1
• Consider hemoglobin electrophoresis if thalassemia is suspected, especially with microcytosis out of proportion to the degree of anemia 1
• Inflammatory markers (CRP) should be checked to identify inflammation that may affect iron parameters 1
• Percentage of hypochromic red cells can provide additional information about iron availability over the preceding 2-3 months 1, 4

Management Algorithm

Step 1: Confirm Iron Deficiency

• If ferritin <30 μg/L and/or TSAT <20%, diagnose iron deficiency anemia 1
• If ferritin is 30-100 μg/L with elevated inflammatory markers, consider functional iron deficiency 1

Step 2: Initiate Iron Therapy

• Oral iron supplementation is first-line therapy for uncomplicated iron deficiency anemia 1
• Monitor response to iron therapy - a good response (Hb rise ≥10 g/L within 2 weeks) confirms iron deficiency 1
• Continue iron therapy for 3 months after hemoglobin normalization to replenish iron stores 1

Step 3: Investigate Underlying Cause

• In adults, gastrointestinal sources of blood loss should be investigated (upper and lower GI endoscopy) 1
• In women of reproductive age, assess for heavy menstrual bleeding 1
• Consider other causes of iron malabsorption such as celiac disease 1

Step 4: Monitor Thrombocytosis

• Thrombocytosis should resolve with correction of iron deficiency 1
• If thrombocytosis persists after iron repletion, consider alternative diagnoses including inflammatory conditions or primary hematologic disorders 1

Special Considerations

Differential Diagnosis

• Thalassemia trait: typically shows more pronounced microcytosis with normal or elevated RBC count and minimal anisocytosis 1, 3
• Anemia of chronic disease: may present with hypochromia but typically has normal or low TSAT with normal or elevated ferritin 1
• Sideroblastic anemia: can present with hypochromia and variable RDW 1

Pitfalls to Avoid

• Don't assume all microcytic, hypochromic anemias are iron deficiency - consider thalassemia traits, especially in appropriate ethnic populations 1
• Don't miss concurrent B12 or folate deficiency, which can mask the microcytosis of iron deficiency by causing macrocytosis 1
• Don't overlook inflammation as a cause of functional iron deficiency with reactive thrombocytosis 1
• Don't rely solely on ferritin in the setting of inflammation - use multiple parameters including TSAT and response to iron therapy 1

Monitoring Response

• Reticulocyte count should increase within 7-10 days of starting iron therapy 1
• Hemoglobin should rise by approximately 10 g/L every 2 weeks 1
• RDW may initially increase further as new, larger reticulocytes enter circulation 2
• Platelets should normalize as iron deficiency resolves 1