What systemic disorder is indicated by increased erythropoietin levels with normal PaO2?

Increased erythropoietin levels with normal partial pressure of oxygen (PaO2) suggest a systemic disorder characterized by the body's response to conditions that stimulate red blood cell production without the presence of hypoxia. In this scenario, secondary polycythemia is the most appropriate diagnosis. Secondary polycythemia occurs when there is an overproduction of erythropoietin, typically due to underlying conditions, such as tumors or other diseases, that can stimulate erythropoietin secretion independent of oxygen saturation levels.

Normal PaO2 indicates that the oxygen levels in the blood are adequate, which rules out hypoxia as a driving factor for erythropoietin production. In primary polycythemia, also known as polycythemia vera, the increased cell production is due to a myeloproliferative disorder and not elevated erythropoietin levels. Conditions like chronic obstructive pulmonary disease (COPD) would more commonly present with elevated erythropoietin due to hypoxia rather than a normal PaO2. Acute renal failure can lead to varied erythropoietin levels but is often associated with different clinical features rather than isolated erythropoietin elevation in the context of normal oxygen.

Thus