What is the recommended work‑up for a 17‑year‑old adolescent with anemia (hemoglobin 9.1 g/dL), low mean corpuscular volume, low mean corpuscular hemoglobin concentration, and increased red‑cell distribution width?

Anemia Work-Up in a 17-Year-Old with Microcytic Anemia and Elevated RDW

This 17-year-old with hemoglobin 9.1 g/dL, low MCV, low MCHC, and high RDW most likely has iron deficiency anemia, and the initial work-up should include serum ferritin, transferrin saturation (TSAT), reticulocyte count, and C-reactive protein (CRP) to confirm the diagnosis and assess for concurrent inflammation. 1

Initial Laboratory Assessment

The combination of microcytic anemia (low MCV, low MCHC) with elevated RDW strongly suggests iron deficiency, as this pattern reflects both small red cells and increased variation in cell size—a hallmark of iron-restricted erythropoiesis 2, 3. The elevated RDW is particularly useful here, as it helps distinguish iron deficiency from thalassemia trait, which typically presents with low MCV but normal RDW 4, 5.

Minimum Required Tests

• Serum ferritin: The most powerful single test for iron deficiency 6, 7

  • In adolescents without inflammation: ferritin <15-30 μg/L confirms iron deficiency 4, 1
  • If inflammation is present (elevated CRP): ferritin up to 100 μg/L may still indicate iron deficiency 1

• Transferrin saturation (TSAT): Calculate from serum iron and total iron-binding capacity 2

  • TSAT <15-16% supports iron deficiency 2, 6

• Reticulocyte count: Essential to assess bone marrow response 2, 1

  • Low or inappropriately normal reticulocyte index (<2.0) indicates decreased RBC production, consistent with iron deficiency 2
  • Elevated reticulocytes would suggest blood loss or hemolysis requiring different evaluation 2, 1

• CRP: Needed to interpret ferritin accurately in the presence of inflammation 1

Peripheral Blood Smear Review

A visual review of the peripheral blood smear is critical to confirm microcytosis, assess red cell morphology (hypochromia, anisocytosis), and exclude other causes such as thalassemia or sideroblastic anemia 2.

Clinical History and Physical Examination

Focus on specific risk factors and signs rather than general symptoms 2:

Key Historical Elements to Elicit

• Dietary assessment: Iron intake from meat, fortified foods; restrictive diets 4, 7
• Menstrual history (if female): Heavy or prolonged menstrual bleeding 2, 4
• Gastrointestinal symptoms: Blood in stool, abdominal pain, diarrhea suggesting malabsorption or blood loss 2, 6
• Medication use: NSAIDs, aspirin, proton pump inhibitors 6, 7
• Family history: Thalassemia, hereditary anemias 2
• Ethnicity: Increased thalassemia risk in Mediterranean, Asian, African populations 4

Physical Examination Findings

• Pallor, tachycardia, signs of heart failure in severe anemia 2
• Jaundice, splenomegaly (suggests hemolysis, not typical for iron deficiency) 2
• Neurologic symptoms (would suggest B12 deficiency, not expected here) 2
• Signs of gastrointestinal pathology 6

Diagnostic Algorithm Based on Initial Results

If Ferritin <30 μg/L and TSAT <15% (No Inflammation)

• Diagnosis confirmed: Iron deficiency anemia 2, 6, 7
• Proceed to identify underlying cause (see below)

If Ferritin 30-100 μg/L with Elevated CRP

• Likely iron deficiency with concurrent inflammation (anemia of chronic disease component) 1
• Consider additional testing: soluble transferrin receptor, reticulocyte hemoglobin content 7

If Ferritin >100 μg/L

• Iron deficiency unlikely; consider anemia of chronic disease, thalassemia, or other causes 1
• Hemoglobin electrophoresis to exclude thalassemia 2, 4

Identifying the Underlying Cause

Once iron deficiency is confirmed, determine the etiology 6, 7:

For Adolescent Males or Post-Menarchal Females with Heavy Menses

• Menstrual assessment is priority in females 4
• Gastrointestinal evaluation if inadequate menstrual explanation or in males 6
  • Stool guaiac testing 2
  • Testing for Helicobacter pylori 7
  • Consider celiac serology (tissue transglutaminase IgA with total IgA) 7, 8
  • Upper endoscopy with duodenal biopsies and colonoscopy if blood loss suspected or celiac disease possible 6, 7

Dietary Assessment

• Evaluate for inadequate iron intake, particularly in vegetarians or those with restricted diets 4, 7, 8
• Assess for consumption of >24 oz cow's milk daily (can impair iron absorption) 4

Extended Work-Up if Initial Tests Are Inconclusive

If the diagnosis remains unclear after initial testing 1:

• Vitamin B12 and folate levels: To exclude combined deficiency (though macrocytosis would be expected) 2, 1
• Lead level: If environmental exposure suspected 4
• Hemoglobin electrophoresis: To definitively exclude thalassemia trait 2, 4
• Hematology consultation: For complex cases or suspected bone marrow disorders 7

Common Pitfalls to Avoid

• Do not assume all microcytic anemia is iron deficiency: Thalassemia trait is common in certain ethnic groups and presents with low MCV but typically normal or only mildly reduced hemoglobin, normal RDW, and elevated RBC count 2, 4, 5

• Do not rely on hemoglobin alone for screening: Hemoglobin and hematocrit are late indicators of iron deficiency; tissue iron depletion occurs first 4, 3

• Do not misinterpret ferritin in inflammation: Ferritin is an acute phase reactant and may be falsely elevated despite true iron deficiency when inflammation is present 2, 1, 6, 1

• Do not overlook celiac disease: This is a common cause of iron deficiency in adolescents due to malabsorption and should be tested for, especially if gastrointestinal symptoms are present 7, 8

• Do not start empiric iron therapy without confirming the diagnosis: While presumptive treatment may be appropriate in young children with clear risk factors, adolescents warrant full evaluation to exclude other causes and identify underlying pathology 4, 9