Differential Diagnosis for Elevated Hematocrit with Elevated MCV

• Single Most Likely Diagnosis
  • Dehydration: This is the most common cause of an elevated hematocrit, as it reduces plasma volume, thereby concentrating red blood cells. An elevated MCV (Mean Corpuscular Volume) could be seen in dehydration due to the relative increase in larger red blood cells as smaller ones are lost or destroyed.
• Other Likely Diagnoses
  • Polycythemia Vera: A myeloproliferative disorder characterized by the overproduction of red blood cells, white blood cells, and platelets. It can cause an elevated hematocrit and may also result in an elevated MCV due to the variability in red blood cell size.
  • Chronic Lung Disease: Conditions like chronic obstructive pulmonary disease (COPD) can lead to hypoxia, stimulating erythropoietin production and thus increasing red blood cell production, which can elevate hematocrit. The MCV might be elevated due to the body's attempt to increase oxygen delivery.
• Do Not Miss Diagnoses
  • Carbon Monoxide Poisoning: Although less common, carbon monoxide poisoning can cause an elevated hematocrit due to carboxyhemoglobin formation, which does not deliver oxygen to tissues, potentially leading to an increase in erythropoietin and thus red blood cell production. The MCV could be elevated in the setting of increased red blood cell turnover.
  • Erythropoietin-Producing Tumors: Rare tumors that produce erythropoietin can lead to secondary polycythemia, characterized by an elevated hematocrit. The MCV might be elevated due to the increased production of red blood cells.
• Rare Diagnoses
  • Primary Familial Polycythemia: A rare genetic disorder leading to increased sensitivity of erythroid progenitor cells to erythropoietin, resulting in elevated hematocrit. The MCV could be elevated due to the increased red blood cell production.
  • High-Altitude Adaptation: Prolonged exposure to high altitudes can lead to an increase in red blood cell production (and thus hematocrit) as an adaptation to lower oxygen levels. The MCV might be elevated as part of this adaptive response.