What is the workup for elevated hemoglobin (H/H) and hematocrit (Hct) on laboratory results?

From the Guidelines

The workup for elevated hemoglobin and hematocrit (H/H) should begin with a thorough history and physical examination, followed by targeted laboratory testing to determine the underlying cause and guide management. This approach is crucial in identifying potential secondary causes of elevated H/H, such as smoking, high-altitude living, sleep apnea, chronic lung disease, and certain medications 1.

Initial Steps

• Confirm the elevation with repeat testing and review past values to determine if this is acute or chronic
• Order a complete blood count with peripheral smear, comprehensive metabolic panel, erythropoietin level, and arterial blood gas to assess for hypoxemia
• Consider JAK2 V617F mutation testing if polycythemia vera is suspected ### Evaluating Secondary Causes
• Evaluate for secondary causes including smoking, high-altitude living, sleep apnea, chronic lung disease, and certain medications
• If dehydration is suspected, provide hydration and recheck values
• In acquired secondary polycythemia, initial laboratory tests should include the measurement of arterial hemoglobin-oxygen saturation and the carboxyhemoglobin level, especially in smokers 1 ### Management
• For significant elevations, especially with symptoms like headache, dizziness, or visual disturbances, therapeutic phlebotomy may be indicated to reduce blood viscosity
• Remove 500mL of blood over 30-45 minutes and repeat as needed to achieve target hematocrit below 45%
• Specific management of secondary polycythemia depends on the underlying cause and should take into account the balance between the physiological benefit of an increased hematocrit level and the possible impairment of oxygen delivery to tissues as a result of increased whole blood viscosity 1.

Special Considerations

• In cyanotic congenital heart disease, aggressive phlebotomy should be avoided because of the potential risk of stroke
• In patients with high oxygen-affinity hemoglobinopathy, judicious phlebotomy to a hematocrit level of 60% is reasonable, may alleviate symptoms of hyperviscosity, and may provide some hemodynamic improvement 1
• Post–renal transplant erythrocytosis is distinctly associated with an increased risk of thrombosis, and treatment with angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor inhibitors may be effective in lowering hematocrit levels 1

From the Research

Elevated Hemoglobin/Hematocrit on Labs

Elevated hemoglobin/hematocrit on labs can be an indication of several conditions, including polycythemia vera (PV).

• PV is a myeloproliferative neoplasm characterized by an increased red blood cell mass and increased risk of thrombosis 2, 3.
• The diagnosis of PV is based on the presence of erythrocytosis, which is defined as a hemoglobin level greater than 16.5 mg/dL in men or greater than 16.0 mg/dL in women 2.
• Other common features of PV include thrombocytosis, leukocytosis, pruritus, erythromelalgia, transient visual changes, and splenomegaly 2, 3.

Treatment of Polycythemia Vera

The treatment of PV typically involves a combination of therapeutic phlebotomy and low-dose aspirin, as well as cytoreductive therapy in high-risk patients 2, 3, 4.

• Therapeutic phlebotomy is used to reduce the red blood cell mass and decrease the risk of thrombosis 2, 5, 6.
• Cytoreductive therapy, such as hydroxyurea or interferon, is used to reduce the production of red blood cells and decrease the risk of thrombosis 2, 3, 4.
• Ruxolitinib, a Janus kinase inhibitor, can be used in patients who are intolerant of or resistant to hydroxyurea 2, 3.

Risk of Thrombosis

The risk of thrombosis is a major concern in patients with PV, and can be reduced with therapeutic phlebotomy and cytoreductive therapy 2, 3, 5, 6.

• Patients who require frequent phlebotomies are at higher risk of thrombosis 5.
• The use of hydroxyurea and phlebotomy can reduce the risk of thrombosis, but may also increase the risk of extrahematologic toxicity 5.
• The impact of phlebotomy and hydroxyurea on survival and risk of thrombosis among older patients with PV has been studied, and both treatments have been shown to be effective in reducing the risk of thrombosis and improving overall survival 6.