Iron Studies Should Be Ordered
For a 15-year-old female with hemoglobin 11.8 g/dL and hematocrit 35.2%, the essential next test is a complete iron panel including serum ferritin, transferrin saturation, serum iron, and total iron-binding capacity (TIBC), along with C-reactive protein (CRP) to assess for inflammation. 1
Why This Patient Has Anemia
This adolescent meets WHO criteria for mild anemia in females ≥15 years (hemoglobin 11.0–11.9 g/dL or hematocrit <36%), making iron deficiency the most likely diagnosis given her age and sex. 1 The normal AST of 11 IU/L effectively excludes liver disease as a contributing cause, since hepatic disorders typically raise AST 2–6-fold above normal. 1
The Critical Diagnostic Tests Needed
First-Line Iron Studies (All Required)
Serum ferritin <30–35 µg/L indicates depleted iron stores when inflammation is absent and is the single most reliable marker for iron deficiency. 1
Transferrin saturation <15–16% supports iron deficiency and is less affected by acute inflammation than ferritin, helping differentiate true iron deficiency from anemia of chronic disease. 2, 1
Total iron-binding capacity (TIBC) >45 µmol/L provides additional confirmation of iron deficiency. 1
C-reactive protein (CRP) must be measured concurrently because ferritin rises as an acute-phase reactant during inflammation; a normal CRP is required to interpret low ferritin accurately. 1
Why Iron Deficiency Is So Common in This Population
Adolescent females aged 14–18 years face exceptionally high risk for iron deficiency—prevalence can exceed 50% in some cohorts—due to menstrual blood loss, rapid growth spurts, and typical dietary iron intake below the recommended 15 mg/day. 1 Iron deficiency affects approximately 7.8 million adolescent females and women of childbearing age in the United States. 1
Common Pitfalls to Avoid
Do not rely on ferritin alone without CRP—inflammation can falsely elevate ferritin and mask true iron deficiency, leading to missed diagnoses. 1
Do not assume normal hemoglobin excludes iron deficiency—up to 50% of individuals with iron deficiency may have normal hemoglobin levels despite ongoing depletion of iron stores. 3
Do not order only a CBC without iron studies—many cases of iron depletion are missed when clinicians rely solely on hemoglobin and hematocrit, which decrease only when severe iron depletion is present. 4
Additional Helpful Tests
Reticulocyte count: A low or inappropriately normal reticulocyte response suggests inadequate bone marrow compensation for anemia, consistent with iron deficiency. 1
Red cell indices (MCV, MCH, MCHC, RDW): Low MCH is the most sensitive early marker of iron deficiency, even before microcytosis develops. 1
What to Do After Confirming Iron Deficiency
Re-measure hemoglobin four weeks after initiating oral iron therapy (typically 100 mg elemental iron daily); an increase of ≥1 g/dL indicates true iron-deficiency anemia and adequate therapeutic response. 1
If hemoglobin does not rise despite documented adherence, screen for celiac disease with tissue transglutaminase (tTG) antibodies and evaluate for gastrointestinal blood loss. 1
Continue iron supplementation for 3–6 months after hemoglobin normalizes to replenish body iron stores. 1
If Iron Studies Are Normal
When iron studies return normal despite anemia, consider:
Vitamin B12 and folate deficiency: Order serum B12 and folate levels. 1
Hemoglobinopathies: Perform hemoglobin electrophoresis when microcytosis is present and the patient belongs to an at-risk ethnic group (African, Mediterranean, Southeast Asian ancestry). 1
Celiac disease: Measure IgA tissue transglutaminase antibodies with total serum IgA to ensure assay adequacy. 3
Hypothyroidism: Check TSH and free T4, as thyroid dysfunction can cause unexplained anemia. 3