How do I interpret this CBC (Hb 12.4 g/dL, Hct 39.5%, MCV 81.6 fL, MCH 25.6 pg, RDW‑CV 17.3%, normal WBC and platelet counts) showing mild isolated anemia, and what are the appropriate next steps?

CBC Interpretation: Mild Normocytic Anemia with Elevated RDW

This CBC shows mild normocytic anemia (Hb 12.4 g/dL, MCV 81.6 fL) with an elevated RDW-CV (17.3%), indicating a heterogeneous red cell population that requires systematic evaluation with iron studies, reticulocyte count, and assessment for chronic disease or occult blood loss. 1

Key Abnormal Findings

• Hemoglobin 12.4 g/dL (Low): Meets criteria for mild anemia (Hb ≤11.9 g/dL and ≥10.0 g/dL by strict definition, though this is borderline) 2
• MCH 25.6 pg (Low): Suggests reduced hemoglobin content per cell 2
• RDW-CV 17.3% (High): Significantly elevated (normal 10.8-15.6%), indicating marked red cell size variation 3
• Normal WBC and platelet counts: Rules out pancytopenia or multi-lineage bone marrow failure 1

Morphologic Classification

This represents normocytic anemia at the lower end of the MCV range (81.6 fL, normal 80-96 fL), which suggests hemorrhage, hemolysis, bone marrow failure, anemia of chronic inflammation, or early renal insufficiency as potential causes. 2

The elevated RDW-CV is particularly important because it indicates a mixed population of red cells, which can distinguish iron deficiency from thalassemia trait or anemia of chronic disease, and may suggest early nutritional deficiency or a dimorphic anemia 3.

Critical Next Steps

Essential Laboratory Tests

Order the following tests immediately to determine the underlying cause: 1

• Iron studies (serum iron, total iron binding capacity/TIBC, transferrin saturation, ferritin): Absolute iron deficiency is indicated by transferrin saturation <15% and ferritin <30 ng/mL 2. This is the most common cause of microcytic anemia and can present with borderline-normal MCV early in the disease 2

• Reticulocyte count (with reticulocyte index): This distinguishes decreased RBC production (low RI <1.0-2.0) from increased destruction or blood loss (high RI) 2. A low reticulocyte index suggests iron deficiency, vitamin B12/folate deficiency, or bone marrow dysfunction 2

• Comprehensive metabolic panel with creatinine: Essential to evaluate for chronic kidney disease, which causes normocytic anemia through decreased erythropoietin production 2, 1

• Inflammatory markers (CRP, ESR): Assess for anemia of chronic disease/inflammation, which can elevate ferritin despite true iron deficiency 1

• Vitamin B12 and folate levels: Rule out nutritional deficiencies that can cause anemia 2, 1

• Thyroid function tests (TSH): Hypothyroidism is a reversible cause of anemia 1

• Stool guaiac test: Screen for occult gastrointestinal bleeding, especially if iron deficiency is confirmed 2, 1

Clinical Assessment Required

Obtain a focused history addressing: 2

• Duration and onset of symptoms (fatigue, exercise dyspnea, chest pain, headache, vertigo, palpitations)
• Menstrual history in women (heavy or prolonged bleeding)
• Medication exposure (NSAIDs, anticoagulants, chemotherapy)
• Family history of anemia, hemoglobinopathies, or thalassemia
• Dietary history (iron, B12, folate intake)
• Chronic diseases (kidney disease, inflammatory conditions, malignancy)
• Signs of bleeding (melena, hematochezia, hematemesis)

Physical examination should focus on: 2

• Pallor, jaundice, petechiae
• Splenomegaly or hepatomegaly
• Cardiac murmurs
• Neurologic abnormalities (B12 deficiency)
• Signs of chronic disease

Interpretation of the Elevated RDW

The markedly elevated RDW-CV (17.3%) is a critical finding that suggests: 3

• Early iron deficiency: Even with borderline-normal MCV, elevated RDW can detect iron deficiency before frank microcytosis develops 3
• Mixed deficiency states: Concurrent iron and folate/B12 deficiency can produce a dimorphic population 3
• Anemia of chronic disease with concurrent iron deficiency: Inflammation can mask iron deficiency 2

This elevated RDW improves the distinction between iron deficiency anemia (high RDW) and thalassemia trait (normal RDW), and between iron deficiency and anemia of chronic disease (which typically has normal or mildly elevated RDW) 3.

Common Pitfalls to Avoid

• Do not assume normal iron stores based on MCV alone: The MCV is at the lower end of normal (81.6 fL), and with the low MCH and elevated RDW, early iron deficiency remains highly likely 4, 3

• Do not rely on hemoglobin/hematocrit alone: These decrease only with severe iron depletion and can miss early deficiency states 4

• Do not overlook functional iron deficiency: In chronic inflammation, ferritin may be falsely elevated as an acute-phase reactant, masking true iron deficiency 2. Transferrin saturation <20% with ferritin 30-100 ng/mL suggests functional iron deficiency 2

• Do not ignore the normal WBC and platelet counts: This isolated red cell pathology makes primary bone marrow disorders less likely but does not exclude them entirely 1

Risk Stratification

This patient requires prompt evaluation because: 2

• Any hemoglobin decrease of 2 g/dL or more from baseline warrants assessment 2
• Symptoms of anemia (if present) negatively impact quality of life and may indicate cardiovascular compromise 2, 1
• Untreated anemia can progress and lead to increased morbidity, particularly in patients with cardiovascular disease 1