Normocytic Anemia with Elevated RDW: Likely Early Iron Deficiency or Mixed Deficiency
This patient has a normocytic anemia (MCV 81.8 fL) with elevated RDW (16.8%), which most commonly indicates early iron deficiency, mixed nutritional deficiencies, or chronic disease with superimposed iron deficiency. The elevated RDW is the critical finding here that distinguishes this from simple chronic disease anemia.
Key Laboratory Interpretation
The CBC shows:
- Moderate anemia (HGB 7.4 g/dL, HCT 23.4%)
- Borderline low-normal MCV (81.8 fL) - technically normocytic but trending toward microcytic
- Elevated RDW (16.8%) - indicating significant red cell size heterogeneity (anisocytosis)
- Low MCH and MCHC - suggesting hypochromia
This pattern represents active erythropoiesis with heterogeneous red cell populations, characteristic of evolving iron deficiency before frank microcytosis develops 1.
Diagnostic Algorithm
Step 1: Iron Studies (Mandatory First-Line)
Order immediately 2:
- Serum ferritin (tissue iron stores)
- Transferrin saturation (available iron for erythropoiesis)
- Serum iron and TIBC
The elevated RDW with borderline-normal MCV has 77.1% sensitivity for iron deficiency anemia, with RDW increasing progressively as iron deficiency develops even before MCV drops 1. In iron deficiency, RDW averages 15.6% compared to 12.7% in normal individuals 1.
Step 2: Assess for Gastrointestinal Blood Loss
If iron deficiency is confirmed, evaluate for GI bleeding 2:
- Fecal occult blood testing
- Consider upper and lower endoscopy depending on age, symptoms, and risk factors
- This is critical because iron deficiency in non-menstruating adults without known blood loss mandates GI evaluation
Step 3: Complete Blood Count Analysis
The normal WBC (4.25) and presumably normal platelets suggest single cell line involvement, making primary bone marrow disorders less likely 2. If two or more cell lines were abnormal, hematology consultation would be warranted 2.
Step 4: Reticulocyte Count
Order to assess bone marrow response 2:
- Low reticulocyte count with iron deficiency = absent/unavailable iron
- Inappropriately normal/low with adequate iron stores = consider chronic kidney disease, inflammation, or erythropoietin deficiency
Step 5: Additional Testing Based on Iron Studies
If iron studies are normal, evaluate for:
- Vitamin B12 and folate levels - mixed deficiencies can present with normal MCV as microcytic and macrocytic processes cancel out 3
- Renal function (BUN, creatinine) - anemia of CKD is normochromic/normocytic 2
- Inflammatory markers (CRP, ESR) - chronic disease anemia
- Hemoglobin electrophoresis if appropriate ethnic background
Critical Clinical Pitfalls
Don't dismiss this as "normocytic" anemia: The MCV of 81.8 fL is at the lower end of normal, and the elevated RDW indicates a mixed population with many microcytic cells already present 1, 4.
RDW is the most sensitive early marker: It rises before MCV drops in iron deficiency, showing increased heterogeneity as new iron-deficient cells mix with older normal-sized cells 1.
The combination of low-normal MCV + elevated RDW + low MCH/MCHC strongly suggests iron deficiency even before frank microcytosis appears 4.
Don't overlook dimorphic anemia: If both iron and B12/folate are deficient, the MCV may appear deceptively normal while RDW is markedly elevated 3. This requires checking all nutritional parameters.
Hemoglobin 7.4 g/dL requires urgent evaluation: This degree of anemia warrants prompt workup and consideration of transfusion depending on symptoms, comorbidities, and cardiovascular status.
Most Likely Diagnosis
Iron deficiency anemia in evolution is the leading diagnosis given the constellation of borderline-low MCV, elevated RDW, and reduced MCH/MCHC 1, 4. The RDW of 16.8% falls within the range typical for iron deficiency (mean 15.6% ± 1.7%) and significantly exceeds the normal range (12.7% ± 0.7%) 1.