Anemia Workup: Microcytic Anemia with Elevated RDW
This patient has microcytic anemia (MCV 80 fL, hemoglobin 10 g/dL) with a markedly elevated RDW (39.5%), which strongly suggests iron deficiency anemia requiring immediate iron studies (serum ferritin, transferrin saturation, TIBC) and reticulocyte count as the next diagnostic steps. 1, 2
Key Laboratory Findings Analysis
Anemia Confirmation
- Hemoglobin 10 g/dL meets WHO criteria for anemia in adult women (threshold <12.0 g/dL) 1, 2
- Hematocrit 32% is proportionally decreased 1
Red Cell Indices Point to Microcytic Anemia
- MCV 80 fL is at the lower limit of normal, indicating microcytic tendency 1, 2
- MCH 25.1 pg and MCHC 31.3 g/dL are both reduced, confirming hypochromia 1
- The RDW of 39.5% is dramatically elevated (normal ~11-15%), indicating marked red cell size variation (anisocytosis), which is the hallmark of iron deficiency anemia 1, 2
Other Relevant Findings
- Mildly elevated glucose (114 mg/dL) requires fasting glucose or HbA1c for diabetes screening, but is not the priority 1
- Normal TSH (1.250) rules out thyroid dysfunction as a cause 1
- Normal renal function (eGFR 111) excludes anemia of chronic kidney disease 3
Essential Next Tests
Iron Studies (Highest Priority)
- Serum ferritin: <30 μg/L confirms iron deficiency in the absence of inflammation 1, 2
- Transferrin saturation (TSAT): <15-20% indicates iron deficiency 4, 2
- Total iron-binding capacity (TIBC): elevated in iron deficiency, helps differentiate from anemia of chronic disease 2
- Serum iron level: complements the iron status evaluation 2
Reticulocyte Count
- Low or normal reticulocyte count indicates inadequate bone marrow response, consistent with iron deficiency or anemia of chronic disease 1, 3, 5
- Elevated reticulocyte count would suggest hemolysis or blood loss with adequate marrow response 1, 5
Inflammatory Markers (If Ferritin 30-100 μg/L)
- C-reactive protein (CRP) or ESR to assess for inflammation 4, 1
- Ferritin 30-100 μg/L with elevated CRP suggests combined iron deficiency and anemia of chronic disease 2
- Ferritin >100 μg/L with TSAT <20% indicates anemia of chronic disease 2
Peripheral Blood Smear
- Confirms microcytosis and hypochromia 1, 5
- Identifies red cell morphology abnormalities 1, 6
- May reveal target cells (thalassemia) or pencil cells (iron deficiency) 1
Differential Diagnosis for Microcytic Anemia
Most Likely: Iron Deficiency Anemia
- Extremely elevated RDW strongly favors iron deficiency over thalassemia 1, 2
- Thalassemia typically has normal or only mildly elevated RDW 1
Alternative Diagnoses to Consider
- Anemia of chronic disease: ferritin normal/elevated, low TSAT, presence of inflammation 1, 2
- Thalassemia trait: normal RDW, family history, hemoglobin electrophoresis needed if iron studies normal 1, 2
- Sideroblastic anemia: rare, consider if no response to iron therapy 2
Critical Pitfalls to Avoid
- Ferritin is an acute phase reactant and can be falsely elevated in inflammatory states despite true iron deficiency 1, 2
- In this scenario, ferritin 30-100 μg/L with inflammation still suggests iron deficiency 2
- Do not assume thalassemia without checking iron studies first—the elevated RDW makes iron deficiency far more likely 1, 2
- Mixed anemias can present with normal MCV when microcytosis and macrocytosis coexist, but this patient's indices are consistently microcytic 1
Source of Blood Loss Investigation (If Iron Deficiency Confirmed)
Gastrointestinal Evaluation
- In adult women of reproductive age, menstrual blood loss is the most common cause 3
- In postmenopausal women, bidirectional endoscopy (upper endoscopy and colonoscopy) is recommended to identify GI blood loss 3
- Small bowel evaluation if bidirectional endoscopy negative but transfusion-dependent anemia persists 3