A 7-week-old boy is brought to the office for routine follow-up after being discharged from the neonatal intensive care unit (NICU). He was born at 32 weeks gestation, and the pregnancy was complicated only by preterm labor. After delivery, the patient received a short course of prophylactic antibiotics while awaiting blood culture results, which were negative for bacterial growth. Other than difficulty feeding, he had no other issues in the NICU. By age 6 weeks, the patient was taking a normal volume of fortified preterm formula and gaining weight appropriately. He was discharged from the hospital last week and has continued taking formula and ferrous sulfate. Temperature is 37.5 (99.5 F), pulse is 150/min, and respirations are 30/min. Pulse oximetry is 98% on room air. The patient is awake and alert. Cardiac auscultation reveals a 2/6 systolic flow murmur with no gallop. The abdomen is soft with no organomegaly. Laboratory results are as follows: The peripheral smear shows normocytic, normochromic red blood cells. Which of the following is the most likely underlying cause of this patient's laboratory findings?

Question

A 7-week-old boy is brought to the office for routine follow-up after being discharged from the neonatal intensive care unit (NICU).  He was born at 32 weeks gestation, and the pregnancy was complicated only by preterm labor.  After delivery, the patient received a short course of prophylactic antibiotics while awaiting blood culture results, which were negative for bacterial growth.  Other than difficulty feeding, he had no other issues in the NICU.  By age 6 weeks, the patient was taking a normal volume of fortified preterm formula and gaining weight appropriately.  He was discharged from the hospital last week and has continued taking formula and ferrous sulfate.  Temperature is 37.5 (99.5 F), pulse is 150/min, and respirations are 30/min.  Pulse oximetry is 98% on room air.  The patient is awake and alert.  Cardiac auscultation reveals a 2/6 systolic flow murmur with no gallop.  The abdomen is soft with no organomegaly.  Laboratory results are as follows:  The peripheral smear shows normocytic, normochromic red blood cells.  Which of the following is the most likely underlying cause of this patient's laboratory findings?

Quizplus · Accepted Answer

11ec25c8_d6a9_77f3_bc81_0968f29e323e_MD0003_00 This patient has normocytic, normochromic anemia with a minimal reticulocyte response, which indicates that the bone marrow is not producing adequate red blood cells (RBCs) to compensate for the anemia. The most likely cause in this 7-week-old, preterm infant is anemia of prematurity (AOP). After birth, increased oxygenation (ie, breathing, ductus closure) triggers reduced erythropoietin (EPO) production by the liver and kidney. Low levels of circulating EPO impair erythropoiesis in the bone marrow, which normally causes a mild, transient anemia that reaches a nadir of around 9-11 g/dL at age 2-3 months in term infants (ie, physiologic anemia of infancy). Compared to term infants, preterm infants have a lower initial hematocrit at birth, a shorter erythrocyte life span, and less capacity to produce renal EPO. Therefore, their erythrocyte nadir tends to be more severe (eg, ~7 g/dL) and occur earlier (eg, 1-2 months), resulting in AOP. Frequent phlebotomy in the neonatal intensive care unit can further exacerbate the condition. nadir Many cases of AOP are asymptomatic. However, mild tachycardia is common and a flow murmur, apnea, and poor weight gain also can occur. Laboratory evaluation shows normocytic, normochromic anemia with normal platelets and leukocytes. Although the absolute reticulocyte count may be normal for age, reticulocytosis in response to anemia is absent, as seen in this patient. (Choice A) Anemia due to thalassemia (ie, abnormal alpha or beta globin production) causes hypochromic, microcytic RBCs and abnormal cell morphology (eg, target cells) on peripheral smear. target cells (Choice B) Hemolytic anemia (eg, antibiotic-mediated immune hemolysis) is characterized by increased intra- or extravascular RBC destruction. Subsequent reduced tissue oxygenation drives increased erythropoietin, leading to reticulocytosis. (Choice D) Iron deficiency anemia causes microcytic, hypochromic RBCs and would be less likely in the setting of fortified formula and iron supplementation. (Choice E) Iron sequestration in macrophages is characteristic of anemia of chronic disease, which is marked by normocytic/microcytic anemia and poor reticulocytosis. However, it is typically due to chronic inflammation, infection, or malignancy and usually occurs in older children and adults. Given the timeline of this patient's anemia and the minimal systemic symptoms, AOP is far more likely. Educational objective: Anemia of prematurity, the most common cause of anemia in preterm infants, results from impaired erythropoietin production. Patients have normocytic, normochromic anemia with minimal reticulocyte response. References: Erythropoiesis and the approach to anemia in premature infants. (http://www.ncbi.nlm.nih.gov/pubmed/23025780)

A 7-Week-Old Boy Is Brought to the Office for Routine