A 52-year-old man with elevated hematocrit
A 52-year-old municipal transit dispatcher visits the clinic after an elevated hemoglobin level was discovered during an employment physical. He notes daytime fatigue and morning sluggishness. His spouse reports loud nightly snoring and gasping. He takes amlodipine for hypertension and does not use tobacco. Body mass index is 37 kg/m2, blood pressure is 146/92 mm Hg, and ambient air oxygen saturation is 96%. The oropharynx has a crowded soft palate. Lungs are clear, and there is no splenomegaly. Laboratory studies: Hemoglobin: 18.9 g/dL, Hematocrit: 57%, Leukocyte count: 6,700/mm3, Platelet count: 242,000/mm3, Serum erythropoietin: 32 mIU/mL (reference range: 4-24 mIU/mL), JAK2 V617F mutation: negative. Renal ultrasonography reveals no abnormalities. Which of the following is the most appropriate next diagnostic test?
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Post-Call Recovery Reads
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A
Explanation
Clinical Pearl:
Secondary erythrocytosis with an elevated serum erythropoietin level, normal diurnal oxygen saturation, and normal renal imaging is most commonly driven by sleep-disordered breathing, which requires nocturnal polysomnography for confirmation.
Explanation:
This patient has secondary erythrocytosis driven by nocturnal episodic hypoxia from upper airway collapse during sleep. In-laboratory nocturnal polysomnography is the standard diagnostic test to confirm sleep-disordered breathing and guide positive airway pressure therapy. Bone marrow aspiration and core biopsy is indicated for primary polycythemia vera, but that diagnosis is excluded by an elevated serum erythropoietin level and the absence of a JAK2 V617F mutation. Contrast-enhanced abdominal computed tomography is unindicated because renal ultrasonography has already excluded an erythropoietin-secreting renal cell neoplasm or hydronephrosis. Qualitative hemoglobin electrophoresis is inappropriate because high-oxygen-affinity hemoglobin variants present at an earlier age and are identified by p50 co-oximetry rather than standard electrophoresis. Resting transthoracic echocardiography evaluates right-to-left intracardiac shunts, which cause persistent daytime arterial hypoxemia that is contradicted by this patient's normal ambient air oxygen saturation of 96%.
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