In three months, his repeat hemoglobin level is 19.0 g/dL. His oxygen saturation in the office is 95% on room air. His carboxyhemoglobin level is normal and serum erythropoietin level is elevated. Iron studies and serum folate and vitamin B12 levels are all normal. Urinalysis shows no blood, no RBCs, and trace protein. Which of the following is the best next step in managing this patient?

Question

In three months, his repeat hemoglobin level is 19.0 g/dL.  His oxygen saturation in the office is 95% on room air.  His carboxyhemoglobin level is normal and serum erythropoietin level is elevated.  Iron studies and serum folate and vitamin B12 levels are all normal.  Urinalysis shows no blood, no RBCs, and trace protein.  Which of the following is the best next step in managing this patient?

Quizplus · Accepted Answer

Explanation: This patient was appropriately evaluated with a repeat serum hemoglobin level followed by measurement of the erythropoietin level. The elevated erythropoietin level essentially eliminates polycythemia vera as a possibility. The most likely cause of this patient's polycythemia is therefore chronic hypoxia. The normal carboxyhemoglobin level excludes carbon monoxide toxicity, which can be a cause of polycythemia in patients who smoke heavily. Since this patient's oxygen saturation is 95% on room air, significant underlying pulmonary disease is unlikely. It is therefore reasonable to consider a source of intermittent hypoxia, the most common of which is sleep apnea. Nocturnal oximetry would be a reasonable test at this point since nighttime hypoxia from sleep apnea is a potential cause of reactive polycythemia. Given his high BMI, obesity hypoventilation could also be contributing his sleep apnea/hypoxia. (Choice A) Bone marrow biopsy can be used to confirm a diagnosis of polycythemia vera, but this diagnosis has been excluded by the elevated serum erythropoietin. (Choice B) Hemoglobin electrophoresis is beneficial when an abnormality in the hemoglobin molecule itself is suspected, such as in sickle cell anemia or the thalassemias. (Choice C) JAK2 mutation testing is sometimes used as a confirmatory test for polycythemia vera, which has already been excluded by the elevated serum erythropoietin. (Choice E) Phlebotomy can help reduce symptoms of polycythemia vera. However, treatment of secondary polycythemia should be directed towards the underlying cause, which has yet to be determined in this case. Educational objective: Chronic hypoxia is the most common cause of secondary polycythemia. Carboxyhemoglobin levels should be obtained to exclude carbon monoxide poisoning in certain patients, including those who smoke heavily. Sleep apnea should be considered in patients with a relatively normal oxygen saturation on physical examination, as the hypoxia may be only intermittently present at night.

In Three Months, His Repeat Hemoglobin Level Is 19