Hematocrit (HCT) is the proportion of red blood cells to the total volume of blood, typically measured as a percentage during a routine complete blood count (CBC). Elevated HCT, known as polycythemia, indicates an abnormally high concentration of red blood cells. This increases the blood’s density and viscosity, raising the risk of serious complications like stroke, heart attack, and blood clots. Addressing high hematocrit levels is important for reducing thrombotic risk and improving cardiovascular health.
Determining the Cause of Elevated Levels
Effective management requires identifying the underlying cause, as treatment strategies vary significantly across the three main categories of polycythemia: primary, secondary, and relative.
Primary Polycythemia
Primary polycythemia, such as Polycythemia Vera (PV), is a rare bone marrow disorder causing excessive and unregulated red blood cell production. This overproduction is often due to an acquired JAK2 gene mutation. It occurs independently of the body’s oxygen needs and typically results in low levels of the hormone erythropoietin (EPO) in the blood.
Secondary Polycythemia
Secondary polycythemia occurs when an external factor stimulates the body to produce more red blood cells in response to chronic low oxygen levels (hypoxia). The kidneys release higher amounts of EPO, signaling the bone marrow to increase production. Common causes include smoking, severe lung diseases like COPD, obstructive sleep apnea, and living at high altitudes. Certain medications, such as testosterone replacement therapy, can also lead to elevated HCT.
Relative Polycythemia
Relative polycythemia is not a true increase in red blood cells but an elevated percentage caused by decreased plasma volume. This is most commonly a result of acute or chronic dehydration, which diminishes the liquid component of the blood. Since the absolute number of red blood cells is normal, addressing the fluid volume is the direct solution for this type of HCT elevation.
Immediate Lifestyle and Dietary Changes
Hydration
Increasing fluid intake is the most immediate and effective action for elevated HCT caused by dehydration or relative polycythemia. Consuming more water helps to restore plasma volume, effectively diluting the concentration of red blood cells and lowering the hematocrit percentage. Adequate hydration supports normal blood flow and is a simple first-line step for individuals with mildly elevated HCT.
Smoking Cessation
Quitting smoking is a necessary step if the HCT elevation is linked to chronic low oxygen levels. The carbon monoxide inhaled from cigarette smoke binds tightly to hemoglobin, reducing the blood’s capacity to transport oxygen efficiently. To compensate for this perceived oxygen deprivation, the body releases more EPO, which drives the bone marrow to create more red blood cells, leading to secondary polycythemia. Eliminating this exposure removes the constant stimulus for overproduction, allowing HCT levels to normalize over time.
Dietary Adjustments
Adjusting dietary iron intake can be beneficial, particularly in cases of primary polycythemia or when phlebotomy is part of the treatment plan. Since iron is an essential component of hemoglobin and red blood cell production, doctors may advise reducing or eliminating iron supplements. Moderating the consumption of foods rich in iron, such as red meat, may be suggested to help limit the building blocks available for new red blood cells.
Alcohol Reduction
Reducing or eliminating excessive alcohol consumption can also play a role in HCT management. High alcohol intake contributes to dehydration, which directly causes relative polycythemia by lowering plasma volume. Heavy, long-term alcohol use can also affect the bone marrow’s function and overall blood cell production, making its reduction a helpful lifestyle modification in managing elevated HCT.
Therapeutic Medical Management
When lifestyle changes are insufficient or the cause is a primary condition like Polycythemia Vera, medical interventions are necessary to reduce HCT levels.
Therapeutic Phlebotomy
Therapeutic phlebotomy, which is essentially a controlled form of bloodletting, is the most common medical procedure used to quickly lower the red blood cell count and blood viscosity. Typically, about 500 milliliters of blood are removed, which directly reduces the total red blood cell mass. The main goal of phlebotomy is to maintain the hematocrit below a specific threshold to minimize the risk of clotting. For patients with Polycythemia Vera, the target HCT is generally maintained strictly below 45 percent, a level shown to reduce the incidence of major thrombotic events. The frequency of phlebotomy varies widely based on the individual’s response, often starting more frequently until the target is reached, then shifting to a maintenance schedule.
Cytoreductive Therapy
For high-risk Polycythemia Vera patients or those who cannot tolerate frequent phlebotomies, cytoreductive medications are often prescribed. These drugs work by suppressing the bone marrow’s ability to produce excessive blood cells. Common agents include:
- Hydroxyurea
- Interferon
- The Janus-associated kinase (JAK) inhibitor Ruxolitinib, which targets the underlying molecular defect in PV.
Adjunctive Treatments and Monitoring
Low-dose aspirin (81 to 100 milligrams daily) is a standard part of the treatment plan for many patients with polycythemia. It helps prevent blood clots by inhibiting platelet function. Regular monitoring via complete blood counts (CBC) is required to track HCT levels and adjust the treatment regimen. This ensures the HCT remains in the safe target range, confirming that the management strategy is effectively reducing the risk of cardiovascular complications.