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Pediatric Anemia: Iron Deficiency and Beyond

Introduction

Anemia is defined as a hemoglobin concentration below the age- and sex-specific normal range and is the most common hematologic abnormality in children worldwide. Iron deficiency anemia (IDA) is the most prevalent nutritional deficiency globally, affecting an estimated 40% of children in developing countries. A systematic approach based on mean corpuscular volume (MCV) and reticulocyte count allows efficient classification and targeted workup.

Age-Specific Hemoglobin Norms

In newborns, normal hemoglobin is 14-24 g/dL (physiologic polycythemia due to fetal erythropoiesis). At 2-6 months, hemoglobin ranges from 9.5-14 g/dL, with a physiologic nadir at 6-8 weeks in term infants known as "physiologic anemia of infancy." From 6 months to 6 years, the range is 11-14 g/dL. From 6-12 years, it is 11.5-15.5 g/dL. In adolescent males, the range is 13-16 g/dL, and in adolescent females, 12-16 g/dL. Premature infants reach their nadir earlier (4-6 weeks) and lower (7-8 g/dL), termed "anemia of prematurity."

Classification by MCV

Microcytic Anemia (Low MCV)

Iron deficiency anemia is the most common cause overall. Thalassemia trait (alpha or beta) should be suspected when MCV is disproportionately low relative to hemoglobin level, with the RBC count often elevated. The Mentzer index (MCV/RBC) less than 13 suggests thalassemia. Lead poisoning causes basophilic stippling on smear. Chronic disease or inflammation can present as microcytic (or normocytic). Sideroblastic anemia is rare and shows ringed sideroblasts on bone marrow examination.

Normocytic Anemia (Normal MCV)

Causes include anemia of chronic disease or inflammation, acute blood loss, transient erythroblastopenia of childhood (TEC, a self-limited condition in children ages 1-4 years with normal MCV, distinguishing it from Diamond-Blackfan anemia), hemolytic anemias (sickle cell disease, hereditary spherocytosis, G6PD deficiency, autoimmune hemolytic anemia), chronic kidney disease (erythropoietin deficiency), and bone marrow infiltration (leukemia, neuroblastoma).

Macrocytic Anemia (High MCV)

Causes include vitamin B12 deficiency (strict vegan diets, pernicious anemia, ileal disease), folate deficiency (malnutrition, malabsorption, medications such as methotrexate and phenytoin), Diamond-Blackfan anemia (congenital pure red cell aplasia presenting in the first year of life with elevated fetal hemoglobin and erythrocyte adenosine deaminase), Fanconi anemia (pancytopenia, skeletal anomalies, cafe-au-lait spots, increased chromosome breakage), hypothyroidism, liver disease, and myelodysplastic syndromes.

<image>Diagnostic algorithm for pediatric anemia organized by MCV classification (microcytic, normocytic, macrocytic) with key differentiating laboratory findings and reticulocyte count branching into decreased production versus increased destruction pathways</image>

Iron Deficiency Anemia -- In Depth

Risk Factors

Dietary risk factors include excessive cow's milk intake (greater than 24 oz/day), prolonged bottle feeding, low dietary iron intake, and exclusive breastfeeding beyond 6 months without iron supplementation. Prematurity and low birth weight result in diminished iron stores. Blood loss can occur through GI sources (cow's milk protein-induced colitis in infants, Meckel diverticulum, hookworm) or menstrual losses in adolescent girls. Malabsorption from celiac disease, inflammatory bowel disease, or H. pylori infection is another important cause.

Clinical Features

Presenting features include pallor, fatigue, irritability, poor feeding, and pica (including pagophagia, the craving for ice). Tachycardia, flow murmur, koilonychia, and angular cheilitis may be found on examination. The neurodevelopmental effects of iron deficiency are particularly concerning, including impaired cognition, attention, and motor development, which may not be fully reversible even after iron repletion.

Diagnosis

The CBC shows low hemoglobin, low MCV, and elevated RDW (which differentiates IDA from thalassemia trait, where RDW is normal). Iron studies reveal low serum iron, low ferritin (less than 12 ng/mL), elevated TIBC, and low transferrin saturation (less than 16%). The reticulocyte count is low, reflecting inadequate production. The peripheral smear shows microcytic, hypochromic RBCs, target cells, and pencil cells. Reticulocyte hemoglobin content (CHr) is an early marker of iron-deficient erythropoiesis.

Treatment

Oral iron (ferrous sulfate at 3-6 mg/kg/day of elemental iron) is given divided 1-3 times daily between meals, with vitamin C to enhance absorption. Reticulocytosis is expected within 48-72 hours, and hemoglobin should rise by 1 g/dL per week. Therapy should continue for 3 months after hemoglobin normalizes to replete stores. If there is no response in 4-6 weeks, the diagnosis should be reassessed (could it be thalassemia?), adherence checked, lead level obtained, and celiac disease screening considered. IV iron (ferric carboxymaltose, iron sucrose) is used for refractory IDA, malabsorption, or intolerance.

Prevention

Term infants should receive iron-fortified formula or iron supplementation at 1 mg/kg/day for breastfed infants starting at 4 months until iron-rich foods are introduced. Preterm infants should receive iron supplementation at 2 mg/kg/day beginning at 2-4 weeks of life. Cow's milk should be limited to less than 24 oz per day after age 12 months. The AAP recommends universal screening with hemoglobin at 12 months of age along with risk assessment.

<image>Peripheral blood smear comparison showing normal red blood cells versus iron deficiency anemia (microcytic, hypochromic with pencil cells and high RDW) versus beta-thalassemia trait (microcytic with target cells and normal RDW) versus megaloblastic anemia (macro-ovalocytes and hypersegmented neutrophils)</image>

Hemolytic Anemias -- Overview

Key Features Suggesting Hemolysis

An elevated reticulocyte count, elevated indirect bilirubin, elevated LDH, and low haptoglobin suggest hemolysis. Peripheral smear findings include spherocytes, schistocytes, sickle cells, and bite cells.

Common Causes

Hereditary spherocytosis is autosomal dominant and presents with splenomegaly, jaundice, and gallstones. The osmotic fragility test or eosin-5-maleimide (EMA) binding test is positive. Treatment includes folic acid supplementation and splenectomy for severe disease. G6PD deficiency is X-linked and causes episodic hemolysis triggered by oxidative stress (fava beans, infections, medications such as sulfonamides, nitrofurantoin, and dapsone). Heinz bodies and bite cells are seen on smear. Autoimmune hemolytic anemia (AIHA) shows a positive direct antiglobulin test (DAT/Coombs) and is treated with corticosteroids.

<image>Illustration showing the reticulocyte production index calculation and its use in classifying anemia as decreased production (low RPI) versus increased destruction/blood loss (high RPI), with examples of conditions in each category</image>

Clinical Pearls

Iron deficiency without anemia is common and can cause neurodevelopmental effects; ferritin is the most sensitive early marker. A trial of iron therapy is both diagnostic and therapeutic for suspected IDA, and results should be rechecked in 4-6 weeks. A reticulocyte count should always be checked when evaluating anemia because it is the most important first branch point in the workup. Lead screening should be considered in any child with unexplained microcytic anemia, especially in high-risk environments. Thalassemia trait does not require treatment, and misdiagnosis as IDA leads to unnecessary and potentially harmful iron supplementation.

References

1. Baker RD, Greer FR, Committee on Nutrition. Diagnosis and Prevention of Iron Deficiency and Iron-Deficiency Anemia in Infants and Young Children (0-3 Years of Age). Pediatrics. 2010;126(5):1040-1050.
2. Lanzkowsky P. Iron-Deficiency Anemia. In: Lanzkowsky's Manual of Pediatric Hematology and Oncology. 6th ed. Academic Press; 2016.
3. Cappellini MD, Motta I. Anemia in Clinical Practice — Definition and Classification: Does Hemoglobin Change with Aging? Semin Hematol. 2015;52(4):261-269.
4. Powers JM, Buchanan GR. Diagnosis and Management of Iron Deficiency Anemia: A Clinical Update. Hematol Oncol Clin North Am. 2014;28(4):729-745.

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