What is the interpretation of a Complete Blood Count (CBC) showing anemia with normocytic indices, elevated Red Cell Distribution Width (RDW), and lymphocytosis?

Interpretation of CBC Results: Mild Anemia with Normocytic Indices and Elevated RDW

This CBC shows mild normocytic anemia with an elevated red cell distribution width (RDW) and absolute lymphocytosis, suggesting possible early iron deficiency or anemia of chronic inflammation requiring further evaluation to determine the underlying cause.

CBC Findings Analysis

• Hemoglobin of 10.6 g/dL indicates mild anemia in a female patient (reference range: 11.1-15.9 g/dL) 1
• Hematocrit of 34.1% is at the lower limit of normal range (34.0-46.6%) 1
• MCV of 89 fL and MCH of 27.6 pg are both within normal limits, indicating normocytic, normochromic indices 1
• MCHC of 31.1 g/dL is slightly below normal range (31.5-35.7 g/dL) 1
• RDW of 16.2% is elevated above normal range (11.7-15.4%), indicating increased red cell size variation (anisocytosis) 1, 2
• Absolute lymphocyte count of 4.3 x10³/uL is elevated above normal range (0.7-3.1 x10³/uL) 1

Clinical Significance

Normocytic Anemia with Elevated RDW

• The combination of normocytic indices with an elevated RDW suggests early or developing iron deficiency anemia before microcytosis has developed 1
• This pattern can also be seen in anemia of chronic inflammation, mixed nutritional deficiencies, or early hemolysis 1
• The elevated RDW with normal MCV represents a state of heterogeneous red cell population that often precedes the development of frank microcytosis in iron deficiency 2, 3

Lymphocytosis

• Absolute lymphocytosis may indicate viral infection, certain chronic infections, or lymphoproliferative disorders 1
• This finding should be interpreted in the clinical context of the patient's symptoms and medical history 1

Recommended Follow-up Testing

Iron Studies

• Serum ferritin, transferrin saturation, and total iron binding capacity (TIBC) to assess iron status 1
• Serum ferritin <12 μg/dl is diagnostic of iron deficiency, though values up to 100 μg/dl don't exclude iron deficiency in the presence of inflammation 1

Reticulocyte Count

• Essential to determine if the bone marrow is responding appropriately to anemia 4
• Low reticulocyte count would suggest decreased production (iron deficiency, anemia of chronic disease) 4
• High reticulocyte count would suggest blood loss or hemolysis 4

Additional Testing Based on Clinical Context

• C-reactive protein (CRP) to assess for underlying inflammation 1
• Vitamin B12 and folate levels if mixed deficiency is suspected 1
• Peripheral blood smear review to confirm anisocytosis and evaluate for other morphologic abnormalities 1
• Stool occult blood testing if gastrointestinal blood loss is suspected 1

Diagnostic Algorithm

1. Confirm anemia is present (hemoglobin <11.1 g/dL in females) 1
2. Classify based on MCV (normocytic in this case) 1
3. Assess RDW (elevated in this case) 2
4. Obtain reticulocyte count to determine if bone marrow response is appropriate 4
5. Check iron studies (ferritin, transferrin saturation) 1
6. Consider inflammatory markers (CRP) 1
7. Evaluate for potential causes based on clinical context:
   • In premenopausal women: menstrual blood loss 1
   • In all patients: gastrointestinal blood loss, malabsorption, poor dietary intake 1
   • Consider chronic disease/inflammation 1

Common Pitfalls

• Normal MCV does not exclude iron deficiency; early iron deficiency often presents with normal MCV and elevated RDW 2, 3
• Serum ferritin can be falsely elevated in inflammatory states despite iron deficiency 1
• Relying solely on hemoglobin without investigating underlying cause can miss significant pathology 1
• Failing to consider mixed deficiency states (e.g., combined iron and B12 deficiency) 1
• Overlooking absolute lymphocytosis, which requires separate evaluation 1