A 16-year-old boy is brought to the emergency department due to 3 weeks of progressive shortness of breath during physical activity. The patient stopped playing golf 2 weeks ago after he became short of breath while walking the course. He also feels more tired and weaker than usual. The patient has had no rash, cough, chest pain, palpitations, dizziness, or fever. His medical history is notable for sickle cell disease; he has had a few hospitalizations for pain crises and an episode of acute chest syndrome. The most recent hospitalization was 6 months ago. The patient's only medication is oxycodone, which he takes intermittently for pain. Temperature is 36.7 C (98.1 F), blood pressure is 120/70 mm Hg, pulse is 120/min, and respirations are 18/min. Examination shows a tired-appearing but comfortable adolescent with conjunctival pallor. Laboratory results reveal: Which of the following is the most likely underlying mechanism for this patient's laboratory findings?

Question

A 16-year-old boy is brought to the emergency department due to 3 weeks of progressive shortness of breath during physical activity.  The patient stopped playing golf 2 weeks ago after he became short of breath while walking the course.  He also feels more tired and weaker than usual.  The patient has had no rash, cough, chest pain, palpitations, dizziness, or fever.  His medical history is notable for sickle cell disease; he has had a few hospitalizations for pain crises and an episode of acute chest syndrome.  The most recent hospitalization was 6 months ago.  The patient's only medication is oxycodone, which he takes intermittently for pain.  Temperature is 36.7 C (98.1 F), blood pressure is 120/70 mm Hg, pulse is 120/min, and respirations are 18/min.  Examination shows a tired-appearing but comfortable adolescent with conjunctival pallor.  Laboratory results reveal:  Which of the following is the most likely underlying mechanism for this patient's laboratory findings?

Quizplus · Accepted Answer

11ec25c8_d69a_3587_bc81_4f6ed7068dd4_MD0003_00 This patient has progressive exertional dyspnea, fatigue, pallor, and generalized weakness due to severe anemia. The most likely cause of macrocytic anemia (mean corpuscular volume >100 μm³) in this patient with sickle cell disease (SCD) is folate deficiency. SCD is a chronic hemolytic anemia in which red blood cells are typically normocytic and normochromic with a compensatory elevated reticulocyte count. Without adequate folic acid supplementation or intake, chronic hemolysis can lead to folate deficiency, as the bone marrow uses folate in an attempt to produce red blood cells. Folate deficiency results in laboratory findings of macrocytic anemia and hypersegmented neutrophils. Due to ineffective erythropoiesis, the expected reticulocytosis is absent and an inappropriately low reticulocyte count is seen (ie, low corrected reticulocyte count). Although this patient's reticulocyte count appears normal (0.5%-1.5%), it is lower than expected for SCD. corrected reticulocyte count Adequate folic acid intake via diet or supplementation is recommended to correct the underlying folate deficiency. (Choice A) Although several drugs (eg, methotrexate, hydroxyurea) can lead to macrocytosis, this patient is taking only oxycodone. (Choice B) In patients with SCD, aplastic crisis typically occurs due to parvovirus B19 infection. Erythropoiesis is halted, resulting in severe, acute (<2 weeks) normocytic anemia with decreased reticulocyte count. This patient's macrocytosis and prolonged 3-week course make folate deficiency more likely. (Choice D) Hyperhemolytic crisis in SCD refers to severe, acute, normocytic hemolytic anemia with increased reticulocytosis. In contrast, this patient has macrocytic anemia without an increased reticulocyte count. (Choice E) Splenic sequestration (due to splenic vaso-occlusion and red blood cell pooling) presents in patients with SCD as a rapidly enlarging spleen, abrupt anemia, and increased reticulocyte count. Splenic sequestration typically occurs in young children prior to autoinfarction of the spleen. Educational objective: Sickle cell disease normally causes normocytic, hemolytic anemia with compensatory reticulocytosis. Chronic hemolysis without adequate folic acid intake increases the risk for folate deficiency, a macrocytic anemia with an inappropriately low reticulocyte count. References: Evaluation of macrocytic anemias. (http://www.ncbi.nlm.nih.gov/pubmed/26404440) Evaluation of anemia in children. (http://www.ncbi.nlm.nih.gov/pubmed/20540485) Sickle cell disease. (http://www.ncbi.nlm.nih.gov/pubmed/20301551)

A 16-Year-Old Boy Is Brought to the Emergency Department Due