What is the diagnosis and treatment for a patient with microcytic anemia and elevated RDW?

Diagnosis and Treatment of Microcytic Anemia with Elevated RDW

The laboratory findings indicate iron deficiency anemia (IDA) as evidenced by microcytosis (MCV at lower limit of normal), low MCH, low MCHC, and elevated RDW. 1

Interpretation of Laboratory Values

• RBC count is elevated (5.51 x10^6/uL), which can be a compensatory mechanism in anemia 1
• Hemoglobin (13.1 g/dL) is within normal range but may be relatively low for the patient 1
• MCV is at the lower limit of normal (79 fL), indicating microcytosis 1
• MCH (23.8 pg) and MCHC (30.1 g/dL) are both low, indicating hypochromia 1
• RDW is elevated (17.0%), suggesting increased variation in red cell size (anisocytosis) 1

Diagnostic Significance

• The combination of microcytosis with elevated RDW strongly suggests iron deficiency anemia 1
• An elevated RDW (>14.0%) with low MCV is highly indicative of iron deficiency anemia, whereas thalassemia typically presents with low MCV but normal RDW 1
• The elevated RDW distinguishes iron deficiency from thalassemia minor, which typically has more homogeneous red cell population 2, 3
• Studies show that mean RDW in iron deficiency anemia (18.37-20.62%) is significantly higher than in thalassemia (15.76-17.08%) 3, 4

Confirmatory Testing

• Serum ferritin is the most powerful test for confirming iron deficiency 1
• A serum ferritin <12 μg/dL is diagnostic of iron deficiency 1
• In the presence of inflammation, ferritin up to 100 μg/L may still be consistent with iron deficiency 1
• Additional tests to consider include:
  • Transferrin saturation (<30% supports iron deficiency) 1
  • Serum iron (low in iron deficiency) 1
  • Total iron binding capacity (increased in iron deficiency) 1

Underlying Causes to Investigate

• Gastrointestinal blood loss is the most common cause in adult men and post-menopausal women 1
• Common GI causes include:
  • Colonic cancer/polyps 1
  • NSAID use 1
  • Gastric cancer 1
  • Angiodysplasia 1
  • Inflammatory bowel disease 1
• Malabsorption, particularly celiac disease, should be considered 1
• In pre-menopausal women, menstrual blood loss is the most common cause 1
• Poor dietary intake of iron is another potential cause 1

Treatment Approach

• Identify and treat the underlying cause of iron deficiency 1
• Oral iron supplementation is the first-line treatment 1
• A therapeutic response to three weeks of oral iron confirms the diagnosis of iron deficiency 1
• For patients with inflammatory bowel disease or other conditions with inflammation, higher doses of iron may be needed as inflammation can reduce iron absorption 1
• In cases of malabsorption or intolerance to oral iron, intravenous iron may be necessary 1

Monitoring and Follow-up

• Monitor hemoglobin, MCV, and RDW to assess response to treatment 1
• RDW may increase initially during treatment before normalizing 5
• Continue iron therapy for 3-6 months after normalization of hemoglobin to replenish iron stores 1
• If no response to iron therapy after 4 weeks, reassess diagnosis and adherence 1

Pitfalls and Caveats

• Not all patients with iron deficiency have elevated RDW; combined deficiencies (iron plus B12 or folate) may mask typical findings 1
• Thalassemia can sometimes present with elevated RDW, making differentiation from iron deficiency challenging 2, 3
• Anemia of chronic disease can also present with microcytosis and may coexist with iron deficiency 1
• A normal hemoglobin does not exclude iron deficiency, as compensatory mechanisms may maintain hemoglobin levels despite depleted iron stores 1