What are the implications of elevated hematocrit (Hct) with elevated red blood cell (RBC) count?

From the Guidelines

Elevated hematocrit with elevated red blood cell count is a medical emergency that requires immediate attention to reduce the risk of thrombotic events, with a target hematocrit level below 45%. This condition suggests polycythemia, which can be primary (polycythemia vera) or secondary to underlying conditions. Patients should seek prompt medical evaluation for proper diagnosis through blood tests, including complete blood count, erythropoietin levels, and possibly JAK2 mutation testing 1.

Diagnosis and Treatment

Treatment depends on the cause but may include:

• Phlebotomy to reduce blood volume and viscosity
• Medications like hydroxyurea (starting at 500-1000 mg daily) or interferon-alpha (IFN-α) for polycythemia vera, as they have been shown to reduce the risk of thrombotic events and induce a high rate of haematological response 1
• Low-dose aspirin as a cornerstone of therapy to reduce the risk of cardiovascular events, as shown in the European Collaboration on Low-dose Aspirin in Polycythaemia Vera (ECLAP) study 1
• Addressing underlying causes in secondary polycythemia, such as sleep apnea, high-altitude living, or lung disease

Management and Prevention

Patients with elevated hematocrit and red blood cell count should:

• Stay well-hydrated to reduce blood viscosity
• Avoid smoking and alcohol to minimize cardiovascular risk
• Maintain regular follow-up appointments to monitor their condition and adjust treatment as needed
• Be aware of symptoms such as headache, dizziness, visual disturbances, and itching after bathing, which can indicate increased blood viscosity and clotting risk

Key Considerations

The optimal target of HCT levels for reducing vascular events is below 45%, as shown in the CYTO-PV trial 1. A cytoreductive drug should be prescribed in high-risk patients, such as those over 60 years old or with a history of vascular events. Hydroxyurea (HU) is a recommended first-line treatment for high-risk patients, but its potential leukaemogenic risk should be considered, especially in young subjects or those previously treated with other myelosuppressive agents 1.

From the Research

Implications of Elevated Hematocrit (Hct) with Elevated Red Blood Cell (RBC) Count

• Elevated hematocrit and red blood cell count can be indicative of polycythemia, which is a risk factor for thrombosis 2
• The increased thrombotic risk is assumed to be due to the elevated hematocrit and an associated increase in blood viscosity, however, thrombosis does not accompany most types of erythrocytosis 3
• In polycythemia vera, the risk of major vascular ischemic episodes is rather high at hematocrits between 0.45 and 0.50, and the risk of vascular complications is best controlled by maintaining the hematocrit at less than 0.45 and the platelet count below 400 x 10(9)/L 4
• First-line treatments for polycythemia vera include low-dose aspirin and goal-directed phlebotomy to a hematocrit level of less than 45% to reduce thrombotic events, improve quality of life, and prolong survival 5

Diagnostic Considerations

• An absolute erythrocytosis is present when the red cell mass is raised and the hematocrit is elevated above prescribed limits, and can be primary or secondary in nature 6
• Clear simple criteria for polycythemia vera are now defined, and those who do not fulfill these criteria require further investigation depending on the clinical scenario and initial results 6
• The erythropoietin level provides some guidance as to the direction in which to proceed and the order and extent of investigation necessary in an individual patient 6

Management and Treatment

• Phlebotomy does not prevent the aspirin-responsive microcirculatory circulation disturbances in polycythemia vera because thrombocythemia persists, and the microvascular syndrome associated with thrombocythemia is easily and best controlled by low-dose aspirin or by selective reduction of platelet count to normal with low-dose myelosuppressive agents 4
• Cytoreductive therapy, primarily with hydroxyurea, can be added to first-line treatments when indicated, with consideration of second-line agents such as pegylated interferon-alfa, busulfan, and ruxolitinib, depending on the clinical scenario 5