Laboratory Workup for Mild Anemia in a 17-Year-Old Female
Order a complete iron panel including serum ferritin, transferrin saturation, serum iron, and total iron-binding capacity to evaluate for iron deficiency, which is the most common cause of mild anemia in adolescent females. 1, 2
Understanding the Clinical Context
The patient's hemoglobin of 11.8 g/dL meets WHO criteria for mild anemia in women ≥15 years old (defined as hemoglobin 11.0–11.9 g/dL), and the hematocrit of 35.2% is also below the normal threshold of 36% for non-pregnant women. 1 This degree of anemia in an adolescent female strongly suggests iron deficiency, which affects 15–35% of female athletes and is even more prevalent in menstruating adolescents. 1
Essential Laboratory Tests to Order
First-Line Iron Studies (Order All Together)
Serum ferritin is the single most useful test to confirm iron deficiency, with levels <30–35 μg/L indicating depleted iron stores in the absence of inflammation. 1, 2 This is the most established marker for stored iron and should be the cornerstone of your diagnostic workup. 1
Transferrin saturation <15–16% supports iron deficiency and is less affected by acute inflammation than ferritin alone. 1, 2 This helps distinguish true iron deficiency from anemia of chronic disease. 1
Serum iron and total iron-binding capacity (TIBC) complete the iron panel and help calculate transferrin saturation. 1 TIBC >45 μmol/L suggests iron deficiency. 3
C-reactive protein (CRP) should be measured simultaneously because ferritin is an acute-phase reactant that can be falsely elevated during illness or stress, potentially masking iron deficiency. 1, 2 This is critical for proper interpretation of ferritin levels. 1
Additional Helpful Tests
Reticulocyte count evaluates bone marrow response and helps distinguish iron deficiency from other causes of anemia. 1 Low or inappropriately normal reticulocytes indicate inability to respond properly to anemia. 1
Red cell indices from the CBC (MCV, MCH, MCHC, RDW) provide important clues: microcytosis indicates iron-restricted anemia, while normal MCV with low ferritin represents early iron deficiency before red cells become microcytic. 1, 2 Low MCH (mean corpuscular hemoglobin) is actually the most sensitive early marker of iron deficiency, reflecting reduced hemoglobin in newly produced red cells. 2
Reticulocyte hemoglobin content (Ret-He) is an emerging marker that reflects iron availability for current erythropoiesis; values <28 pg indicate iron-deficient red cell production and can detect functional iron deficiency earlier than traditional tests. 4, 5 This test is readily available on automated analyzers and less affected by inflammation. 4
Why This Specific Workup Matters
Adolescent females aged 14–18 years are at particularly high risk for iron deficiency due to menstrual blood loss, rapid growth, and often inadequate dietary iron intake (RDA 15 mg/day for this age group). 1 The prevalence can exceed 50% in some studies of young female athletes. 1
Iron deficiency exists on a spectrum: 1
- Stage 1 (Iron depletion): Low ferritin only, no functional impairment
- Stage 2 (Iron-deficient erythropoiesis): Low ferritin + low transferrin saturation, red cell production affected
- Stage 3 (Iron-deficiency anemia): All of the above + low hemoglobin/hematocrit with microcytic, hypochromic red cells
This patient's mild anemia suggests she is likely in Stage 2 or early Stage 3, making the complete iron panel essential for accurate staging and treatment planning. 1
Common Pitfalls to Avoid
Don't rely on ferritin alone without checking CRP, as inflammation can falsely normalize ferritin levels and cause you to miss true iron deficiency. 1, 2
Don't assume normal MCV rules out iron deficiency—early iron deficiency presents with normal red cell size before stores are completely depleted. 1, 2
Don't order only a CBC thinking the hemoglobin and hematocrit are "close enough to normal"—this patient meets WHO criteria for anemia and requires full evaluation. 1
Don't forget to assess for heavy menstrual bleeding, which is a leading cause of iron deficiency in this population and may require gynecologic evaluation if confirmed. 1
Next Steps After Results
Once iron deficiency is confirmed (ferritin <30–35 μg/L and/or transferrin saturation <15–16%), oral iron supplementation is first-line therapy with approximately 100 mg elemental iron daily. 2 Recheck hemoglobin and iron studies after 1–3 months to assess response, and continue supplementation for 3–6 months after hemoglobin normalizes to replenish body iron stores. 2
If iron studies are normal despite anemia, consider other causes including vitamin B12 and folate deficiency (though less common in this age group), hemoglobinopathies, or chronic disease. 1 In that scenario, additional workup with vitamin B12, folate, and possibly hemoglobin electrophoresis would be warranted. 1