Which laboratory studies and medications should be ordered for a 17‑year‑old female with mild normocytic anemia (hemoglobin 11.8 g/dL, hematocrit 35.2 %, mean corpuscular volume 80 fL) and normal thyroid function?

Laboratory and Medication Orders for a 17-Year-Old Female with Mild Microcytic Anemia

Order serum ferritin, transferrin saturation, and C-reactive protein immediately to confirm iron deficiency anemia, then start oral ferrous sulfate 200 mg three times daily while investigating the source of iron loss. 1

Immediate Laboratory Studies to Order

First-line iron studies:

• Serum ferritin (most specific test; <15 µg/L confirms absent iron stores, <30 µg/L indicates low stores, and 45 µg/L cut-off provides optimal sensitivity/specificity) 1
• Transferrin saturation (TSAT) (<16-20% confirms iron deficiency, especially if ferritin is borderline) 1
• C-reactive protein (CRP) (ferritin is an acute-phase reactant and can be falsely elevated by inflammation) 1

Additional diagnostic tests:

• Reticulocyte count (expected to be low in iron deficiency, reflecting inadequate marrow response) 1
• Peripheral blood smear (to assess red cell morphology and confirm hypochromia) 2

The combination of MCV 80.2 fL (low-normal/borderline low), MCH 26.9 pg (low), MCHC 33.5 g/dL (low-normal), and RDW 14.3% (elevated) strongly suggests iron deficiency anemia rather than thalassemia trait, which typically shows RDW ≤14%. 1

Why Hemoglobin Electrophoresis Is NOT Needed Now

Do not order hemoglobin electrophoresis as a first-line test; it should only be performed if iron studies are normal or borderline, or if the patient fails to respond to iron therapy after 4 weeks. 1 The elevated RDW (14.3%) combined with borderline-low MCV makes iron deficiency far more likely than thalassemia minor. 1

Immediate Treatment: Oral Iron Supplementation

Start ferrous sulfate 200 mg orally three times daily for at least three months after hemoglobin correction to replenish iron stores. 1 This is the first-line treatment for microcytic hypochromic anemia. 1

Alternative formulations if ferrous sulfate is not tolerated:

• Ferrous gluconate 1
• Ferrous fumarate 1
• Add ascorbic acid (vitamin C) to enhance iron absorption 1

Expected response: hemoglobin should rise ≥10 g/L (≥1 g/dL) within 2 weeks, confirming iron deficiency. 1 If this response occurs, continue iron therapy. 1

Critical Next Step: Investigate the Source of Iron Loss

In a 17-year-old female, the two most common causes are heavy menstrual bleeding and gastrointestinal blood loss. 1 However, do not assume menstruation is the sole cause without excluding gastrointestinal pathology. 1, 3

Detailed menstrual history is essential:

• Duration of menses (>7 days suggests menorrhagia)
• Number of pads/tampons per day (>6-8 suggests heavy flow)
• Presence of clots
• Cycle regularity

Dietary assessment:

• Vegetarian or vegan diet (major risk factor for iron deficiency in adolescents) 1
• Inadequate dietary iron intake 1

Gastrointestinal symptoms to assess:

• Melena, hematochezia, or occult bleeding 1
• Abdominal pain, diarrhea, or weight loss (suggesting celiac disease or inflammatory bowel disease) 1

When to Order Additional Studies

If the patient fails to respond to oral iron after 2-4 weeks (hemoglobin rise <1 g/dL):

• Assess compliance with iron therapy 1
• Consider malabsorption (celiac disease screening with tissue transglutaminase antibodies) 1
• Evaluate for ongoing blood loss 1
• Consider intravenous iron if malabsorption is confirmed 1

If iron studies are normal or borderline (ferritin >30 µg/L and TSAT >20%), then order hemoglobin electrophoresis to exclude thalassemia trait. 1

Monitoring Plan

Recheck hemoglobin and hematocrit in 2 weeks to confirm response (expected rise ≥1 g/dL). 1

Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year, then after a further year. 1

Provide additional oral iron if hemoglobin or MCV falls below normal during follow-up. 1

Common Pitfalls to Avoid

Do not overlook combined deficiencies: Iron deficiency can coexist with vitamin B12 or folate deficiency, recognizable by elevated RDW. 1 However, given normal thyroid function and the clinical picture, this is less likely in this adolescent.

Do not attribute iron deficiency solely to dietary insufficiency or menstruation without proper investigation, especially if anemia is moderate-to-severe or fails to respond to therapy. 3

Do not use serum iron alone for diagnosis; it shows considerable day-to-day variability and is less reliable than ferritin and transferrin saturation. 1