What are the causes of elevated hemoglobin (Hb) and hematocrit (Hct)?

From the Guidelines

Elevated hemoglobin and hematocrit levels can result from various conditions, including dehydration, polycythemia vera, chronic hypoxic conditions, certain medications, smoking, kidney diseases, and genetic conditions. The most common cause of elevated hemoglobin and hematocrit is dehydration, which concentrates blood components when fluid volume decreases 1. Other significant causes include:

• Polycythemia vera, a bone marrow disorder causing excessive red blood cell production, which requires medical attention 1
• Chronic hypoxic conditions such as COPD, sleep apnea, and high-altitude living, where the body produces more red blood cells to compensate for reduced oxygen 1
• Certain medications like erythropoietin and anabolic steroids, which can artificially increase red blood cell production 1
• Smoking, which stimulates red blood cell production through carbon monoxide exposure 1
• Kidney diseases, which can elevate levels through increased erythropoietin production 1
• Genetic conditions like polycythemia rubra vera, which can cause inherited elevations 1
• Testosterone-replacement therapy, which can increase hemoglobin levels by 15 to 20 percent 1 It is essential to identify and address the underlying cause of elevated hemoglobin and hematocrit levels, as persistent elevations can increase the risk of blood clots and cardiovascular complications 1. Treatment options may include phlebotomy for polycythemia vera, CPAP for sleep apnea, or simply increasing fluid intake for dehydration. A thorough diagnostic evaluation, including determination of serum EPO and examination of bone marrow histology, is necessary to formulate a working diagnosis of polycythemia vera 1. In cases where the hemoglobin/hematocrit level is higher than the 95th percentile of the normal distribution or accompanied by a PV-related feature, further investigation is warranted 1. Healthcare providers should monitor patients with elevated hemoglobin and hematocrit levels closely, especially in the elderly, as an attendant increase in blood viscosity could aggravate vascular disease 1.

From the Research

Causes of Elevated Hemoglobin (Hb) and Hematocrit (Hct)

• Primary causes:
  • Myeloproliferative neoplasm known as polycythemia vera 2
  • Neoplastic diseases like polycythemia vera with proliferation of a cell clone 3
  • Primary proliferative polycythemia (PPP) 4
• Secondary causes:
  • Excess erythropoietin (EPO) 2
  • Decreased plasma volume 2
  • Chronic hypoxemia 3
  • Reactive forms resulting from chronic hypoxemia 3
  • Smoking 4
• Other causes:
  • Physiologic form of polycythemia in highlanders and athletes training at high altitude 3
  • Erythropoietin and its analogs used as doping substances to induce polycythemia 3
  • Inherited and environmental causes that lead to polycythemia and erythrocytosis 5
  • Relative polycythemia (reduced plasma volume with a normal red cell mass) 4
  • Modifications of the red cell mass and the plasma volume within their normal ranges 4

Diagnostic Considerations

• Measurement of serum EPO levels can guide toward the etiology of polycythemia 2
• Search for JAK2 mutations can aid in diagnosis 2, 6
• Blood volume studies may be necessary to diagnose polycythemia and its cause 4
• Further diagnostic tests, such as bone marrow biopsy and JAK-2 gene mutation test, may be required to confirm the final diagnosis 6