A 10-week-old boy is brought to the clinic for a follow-up visit. He was evaluated in the emergency department 2 weeks ago due to fever. He was well appearing. Laboratory testing revealed leukopenia and anemia. He received empiric antibiotics and was discharged with outpatient follow-up. Bacterial cultures were negative, and his fever resolved. The mother says the patient has been doing well and has continued to normally take soy-based formula feeds. He was born at term, has no other medical conditions, and takes no medications. Temperature is 37 C (98.6 F), blood pressure is 96/62 mm Hg, pulse is 120/min, and respirations are 30/min. Pulse oximetry is 99% on room air. The patient is awake. Physical examination shows no abnormalities. Laboratory results are as follows: Which of the following is the most likely cause of this patient's anemia?

Question

A 10-week-old boy is brought to the clinic for a follow-up visit.  He was evaluated in the emergency department 2 weeks ago due to fever.  He was well appearing.  Laboratory testing revealed leukopenia and anemia.  He received empiric antibiotics and was discharged with outpatient follow-up.  Bacterial cultures were negative, and his fever resolved.  The mother says the patient has been doing well and has continued to normally take soy-based formula feeds.  He was born at term, has no other medical conditions, and takes no medications.  Temperature is 37 C (98.6 F), blood pressure is 96/62 mm Hg, pulse is 120/min, and respirations are 30/min.  Pulse oximetry is 99% on room air.  The patient is awake.  Physical examination shows no abnormalities.  Laboratory results are as follows:  Which of the following is the most likely cause of this patient's anemia?

Quizplus · Accepted Answer

11ec25c8_d6a8_3f6f_bc81_a59f3fe36b3c_MD0003_00 This patient had a fever warranting a complete blood count, which revealed anemia and leukopenia. Repeat evaluation shows resolution of the leukopenia, which therefore was likely due to transient bone marrow suppression in the setting of infection. However, this child's anemia is persistent. In asymptomatic patients age 2-3 months with a normocytic anemia, the most likely cause is physiologic anemia of infancy. age 2-3 months Physiologic anemia of infancy is a transient decline in hemoglobin due to the down-regulation of erythropoietin triggered by a sudden increase in tissue oxygenation at birth. Red blood cell production in the bone marrow slows, leading to a physiologic hemoglobin nadir around 11 g/dL at age 2-3 months in term infants (can be as low as 9 g/dL). Although the absolute value of the reticulocyte count may be normal, a compensatory reticulocytosis in response to anemia is absent. After age 2-3 months, the erythropoietin drive returns and hemoglobin levels rise. physiologic hemoglobin nadir Physiologic anemia of infancy is typically asymptomatic but may be identified on laboratory evaluation for other purposes, as in this case. Findings suggestive of a pathologic cause of anemia, such as hemoglobin <9 g/dL, signs of hemolysis (eg, elevated reticulocyte count), or microcytosis, are not present. (Choice A) Iron deficiency (eg, decreased dietary iron, low iron absorption) causes microcytic anemia (ie, low mean corpuscular volume), which is not seen here. This diagnosis is rare before age 4-6 months because iron stores in young infants are derived from the mother in utero. (Choices B and C) Sickle cell disease, associated with intravascular hemolysis, does not cause anemia until age 4-6 months due to the predominance of fetal hemoglobin in young infants. Moreover, this condition and other hemolytic disorders (eg, glucose-6-phosphatase dehydrogenase deficiency, hereditary spherocytosis) cause a compensatory reticulocytosis in the setting of anemia, which is not seen in this patient. In addition, other common hemoglobinopathies (eg, thalassemia) diagnosed by hemoglobin electrophoresis would cause microcytic, not normocytic, anemia. Educational objective: Physiologic anemia of infancy is an asymptomatic condition characterized by a normal decrease in hemoglobin with a nadir at age 2-3 months. Pathophysiology involves a transient down-regulation of erythropoietin due to increased tissue oxygenation after birth. References: Anemia in infancy. (http://www.ncbi.nlm.nih.gov/pubmed/22474117)

A 10-Week-Old Boy Is Brought to the Clinic for a Follow-Up