Diagnosis and Treatment of Microcytic Anemia with Elevated RDW

Interpretation of Laboratory Values

The patient's RBC count is elevated, which can be a compensatory mechanism in anemia, with a hemoglobin level that may be relatively low for the patient, and an MCV at the lower limit of normal, indicating microcytosis, and MCH and MCHC are both low, indicating hypochromia, and RDW is elevated, suggesting increased variation in red cell size (anisocytosis) 1, 2, 3, 4

The combination of microcytosis with elevated RDW strongly suggests iron deficiency anemia, with an elevated RDW (>14.0%) with low MCV being highly indicative of iron deficiency anemia 1, 2, 4

Serum ferritin is the most powerful test for confirming iron deficiency, with a serum ferritin <12 μg/dL being diagnostic of iron deficiency, and in the presence of inflammation, ferritin up to 100 μg/L may still be consistent with iron deficiency 1, 3, 5, 6
Additional tests to consider include transferrin saturation (<30% supports iron deficiency), serum iron (low in iron deficiency), and total iron binding capacity (increased in iron deficiency) 1, 6

Gastrointestinal blood loss is the most common cause in adult men and post-menopausal women, with common GI causes including colonic cancer/polyps, NSAID use, gastric cancer, angiodysplasia, and inflammatory bowel disease 1, 5, 7
Malabsorption, particularly celiac disease, should be considered, and in pre-menopausal women, menstrual blood loss is the most common cause, and poor dietary intake of iron is another potential cause 1, 5, 7

Identify and treat the underlying cause of iron deficiency, with oral iron supplementation being the first-line treatment, and a therapeutic response to three weeks of oral iron confirms the diagnosis of iron deficiency 1, 5, 7
For patients with inflammatory bowel disease or other conditions with inflammation, higher doses of iron may be needed, and in cases of malabsorption or intolerance to oral iron, intravenous iron may be necessary 1, 5

Monitor hemoglobin, MCV, and RDW to assess response to treatment, and 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

Not all patients with iron deficiency have elevated RDW; combined deficiencies (iron plus B12 or folate) may mask typical findings, and anemia of chronic disease can also present with microcytosis and may coexist with iron deficiency 1, 2, 5
A normal hemoglobin does not exclude iron deficiency, as compensatory mechanisms may maintain hemoglobin levels despite depleted iron stores 1