Laboratory Workup for 17-Year-Old Female with Mild Anemia
Order a complete iron panel including serum ferritin, transferrin saturation (TSAT), total iron-binding capacity (TIBC), and C-reactive protein (CRP) to confirm iron deficiency anemia, which is the most common cause of mild anemia in adolescent females. 1
Clinical Context
Your patient presents with:
- Hemoglobin 11.8 g/dL – meets WHO criteria for mild anemia in females (< 12.0 g/dL) 2, 1
- Hematocrit 35.2% – confirms anemia (< 36%) 1
- Normal comprehensive metabolic panel including AST 11 IU/L, which effectively excludes liver disease as a contributing cause 1
This clinical picture is highly consistent with iron deficiency anemia, which affects 7.8 million adolescent females in the United States, with prevalence exceeding 50% in certain cohorts due to menstrual blood loss, rapid growth, and inadequate dietary iron intake (< 15 mg/day recommended). 1
Required First-Line Laboratory Tests
Iron Studies Panel (Essential)
Serum ferritin < 30–35 µg/L confirms depleted iron stores when inflammation is absent and is the single most reliable marker for iron deficiency 1, 3
Transferrin saturation (TSAT) < 15–16% supports iron deficiency and is less affected by acute inflammation than ferritin, helping differentiate from anemia of chronic disease 1, 3
Total iron-binding capacity (TIBC) > 45 µmol/L indicates 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, 3
Additional Helpful Tests
Reticulocyte count – a low or inappropriately normal reticulocyte response indicates inadequate marrow compensation for anemia, consistent with iron deficiency 1, 3
Red cell indices review – although you have hematocrit 35.2%, review the complete CBC for MCV, MCH, MCHC, and RDW. Low MCH is the most sensitive early marker of iron deficiency even before microcytosis develops 1, 3
Staging Iron Deficiency
Based on combined laboratory findings, iron deficiency progresses through three stages: 1
- Stage 1 (Iron depletion) – low ferritin only, no functional impairment
- Stage 2 (Iron-deficient erythropoiesis) – low ferritin plus low TSAT, indicating impaired red cell production
- Stage 3 (Iron-deficiency anemia) – adds low hemoglobin/hematocrit with microcytic, hypochromic red cells
Your patient with mild anemia is most likely in Stage 2 or early Stage 3, underscoring the need for the full iron panel to stage disease accurately. 1
Critical Pitfalls to Avoid
Do not rely on ferritin alone without CRP – inflammation can falsely elevate ferritin and mask true iron deficiency 1, 3
Do not assume normal MCV excludes iron deficiency – early deficiency may present with normal red cell size 1
Do not limit evaluation to CBC alone – WHO criteria for anemia require full iron studies for proper diagnosis 1
Assess menstrual blood loss as the leading cause in this age group; heavy menstrual bleeding may necessitate gynecologic referral 1
If Iron Studies Are Normal
When iron studies return normal despite anemia, proceed with: 1, 3
- Vitamin B12 and folate levels to evaluate for megaloblastic anemia
- Hemoglobin electrophoresis if microcytosis is present and the patient belongs to an at-risk ethnic group (African, Mediterranean, Southeast Asian ancestry) to rule out thalassemia or other hemoglobinopathies
- Peripheral blood smear to assess red cell morphology
Treatment Monitoring
After confirming iron deficiency: 1
- 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
- If hemoglobin does not rise despite documented adherence, screen for celiac disease (tissue transglutaminase antibodies) and evaluate for gastrointestinal blood loss
- Continue iron supplementation for 3–6 months after hemoglobin normalizes to replenish body iron stores