Workup for Iron Deficiency Anemia in a 12-Year-Old Girl
For a 12-year-old girl with suspected iron deficiency anemia, begin with hemoglobin measurement (anemia defined as <12.0 g/dL at this age), followed by a minimum laboratory workup including complete blood count with red cell indices (MCV, RDW), reticulocyte count, serum ferritin, transferrin saturation, and CRP. 1, 2
Initial Screening and Diagnosis
Hemoglobin Threshold
- Anemia in a 12-year-old girl is defined as hemoglobin <12.0 g/dL (or hematocrit <36%) 1, 2
- This threshold applies to both 12-13 year old children and nonpregnant women 1
Minimum Laboratory Workup
When hemoglobin is below normal, initiate the following tests 1:
- Complete blood count with red cell indices including mean corpuscular volume (MCV) and red cell distribution width (RDW) 1, 2
- Reticulocyte count to assess bone marrow response 1
- Serum ferritin (most specific indicator of iron stores; <15 μg/L confirms iron deficiency) 1, 2
- Transferrin saturation to detect iron-restricted anemia 1
- C-reactive protein (CRP) to identify inflammation that may affect ferritin interpretation 1
Interpreting Red Cell Indices
- Low MCV (microcytosis) indicates iron-restricted anemia or functional iron deficiency 1, 2
- High RDW is an indicator of iron deficiency, particularly useful when microcytosis and macrocytosis coexist 1, 2
- Low or normal reticulocytes with anemia indicate inability to respond properly, suggesting deficiencies or bone marrow disease 1
Extended Workup (If Needed)
If the diagnosis remains unclear after initial testing or if anemia does not respond to treatment after 4 weeks despite compliance, obtain 1:
- Vitamin B12 and folic acid levels (macrocytosis may indicate deficiency) 1
- Haptoglobin and lactate dehydrogenase (to evaluate for hemolysis) 1
- Differential white blood cell count 1
- Consider hematology consultation if cause remains unclear 1
Clinical Assessment Priorities
History Focus
- Menstrual history: Heavy or irregular menstrual bleeding is a major risk factor at this age 3, 4
- Dietary intake: Assess iron-rich food consumption and restrictive eating patterns 1, 3
- Blood loss sources: Recent surgery, trauma, or gastrointestinal symptoms 1
- Medications: Drugs that interfere with iron absorption 1
- Athletic activity: High-level sports participation increases risk 3
Physical Examination Findings
- Pallor (most frequent presenting feature) 5
- In mild-moderate anemia: fatigue, dizziness, weakness, irritability 4, 5
- In severe anemia: tachycardia, shortness of breath, diaphoresis, poor capillary refill 5
Treatment Initiation
Presumptive Treatment Approach
If initial screening shows anemia and you have high clinical suspicion for iron deficiency, you can begin presumptive treatment while awaiting confirmatory tests 1:
- Prescribe 60-120 mg elemental iron daily for adolescent girls 3, 6
- Administer between meals to maximize absorption 2, 3
- Provide dietary counseling emphasizing iron-rich foods and vitamin C co-ingestion 2, 3
Confirmation of Diagnosis
- Recheck hemoglobin after 4 weeks of treatment 1, 2, 6
- An increase of ≥1 g/dL hemoglobin (or ≥3% hematocrit) confirms iron deficiency anemia 1, 2, 6
- If confirmed, continue iron for 2 additional months to replenish stores 1, 2, 6
Common Pitfalls to Avoid
- Do not assume all microcytosis is iron deficiency: Consider thalassemia trait in at-risk populations 6
- Do not stop iron when hemoglobin normalizes: Stores must be replenished over 2-3 months total 3, 6
- Do not ignore lack of response at 4 weeks: This warrants extended laboratory evaluation including MCV, RDW, and ferritin if not already obtained 1, 6
- Recognize that serum ferritin can be falsely elevated in the presence of inflammation (elevated CRP), making interpretation challenging 1