Mild Microcytic Anemia in an 18-Year-Old Female
This patient has mild microcytic anemia (MCV 26.5 × 3 = ~79.5 fL, assuming MCH reflects microcytosis) and should be evaluated for iron deficiency anemia with serum ferritin and transferrin saturation as the first diagnostic step. 1, 2
Diagnostic Approach
Obtain iron studies immediately to determine the etiology of microcytic anemia. 1, 2
- Serum ferritin <30-45 ng/mL confirms iron deficiency anemia in the absence of inflammation and is the single best laboratory parameter for diagnosis. 1, 3, 4
- Transferrin saturation (TSAT) <15% with increased total iron binding capacity (TIBC) further supports iron deficiency. 2, 4
- In an 18-year-old female, iron deficiency is by far the most common cause of microcytic anemia, typically due to menstrual blood loss or dietary insufficiency. 3, 4, 5
Additional Testing Based on Iron Studies
If ferritin is normal or elevated (>45 ng/mL), consider alternative diagnoses:
- Thalassemia trait should be considered if MCV is particularly low (<70 fL) with normal or elevated ferritin, especially in patients of Mediterranean, African, or Southeast Asian descent. 2, 5
- Hemoglobin electrophoresis can differentiate thalassemia from iron deficiency in patients with normal ferritin. 2, 3
- Anemia of chronic disease is less likely in an otherwise healthy 18-year-old but should be considered if inflammatory markers are elevated. 2, 6
Critical Pitfall to Avoid
Ferritin is an acute phase reactant and may be falsely elevated in inflammatory states despite true iron deficiency. 1 If clinical suspicion for iron deficiency remains high despite normal ferritin (e.g., heavy menstrual bleeding), proceed with a trial of iron supplementation or check additional markers like TSAT and TIBC. 1, 4
Treatment for Confirmed Iron Deficiency Anemia
Initiate oral iron supplementation as first-line therapy once iron deficiency is confirmed. 1, 2, 6
- Oral ferrous sulfate 325 mg (65 mg elemental iron) once to three times daily is the standard regimen. 4, 5
- Take iron on an empty stomach to maximize absorption, though taking it with food is acceptable if gastrointestinal side effects occur. 4
- Continue supplementation for 3-6 months after hemoglobin normalizes to fully replete iron stores. 1, 4
- Recheck hemoglobin in 4-6 weeks to confirm response; hemoglobin should increase by 1-2 g/dL if treatment is effective. 4, 5
When to Use Intravenous Iron
Intravenous iron is reserved for specific circumstances and is not typically needed in an otherwise healthy 18-year-old. 1, 6
- Intolerance to oral iron despite multiple formulations. 1, 6
- Malabsorption syndromes (e.g., celiac disease, inflammatory bowel disease). 1, 4
- Ongoing blood loss exceeding oral replacement capacity. 4
Investigate the Underlying Cause
In an 18-year-old female with iron deficiency anemia, focus on menstrual history and dietary intake. 3, 4
- Heavy menstrual bleeding (menorrhagia) is the most common cause in premenopausal women. 4, 5
- Dietary insufficiency (vegetarian/vegan diet, restrictive eating) should be assessed. 4
- Gastrointestinal evaluation is NOT routinely indicated in premenopausal women with an obvious source of blood loss (menstruation) unless there are gastrointestinal symptoms or failure to respond to iron therapy. 1, 2
- Test for H. pylori and celiac disease non-invasively if gastrointestinal symptoms are present or if iron deficiency persists despite adequate supplementation. 1, 2
When to Pursue Endoscopy
Bidirectional endoscopy is strongly recommended for men and postmenopausal women with iron deficiency anemia but is only conditionally recommended for premenopausal women, particularly younger patients like this 18-year-old. 2 Empiric iron supplementation alone is reasonable if she prioritizes avoiding endoscopy risks over detecting rare neoplasia. 2
Monitoring and Follow-Up
Recheck complete blood count and iron studies after 3-6 months of treatment to confirm resolution of anemia and repletion of iron stores. 1, 4