Hematocrit (Hct) and hemoglobin (Hgb) measure the blood’s oxygen-carrying capacity. Hemoglobin is the protein in red blood cells that transports oxygen. Hematocrit is the percentage of total blood volume composed of red blood cells. Elevated levels increase blood viscosity, making the blood thicker. This condition slows blood flow, potentially causing complications like blood clots or reduced oxygen delivery to tissues. Safely lowering Hct and Hgb requires addressing the underlying cause and implementing specific clinical or lifestyle strategies.
Identifying the Underlying Causes of Elevation
Elevated Hct or Hgb, known as erythrocytosis or polycythemia, is usually a response to a physiological need or a disease process. Treatment strategies depend on the specific mechanism of elevation, which is categorized into absolute and relative polycythemia.
Relative polycythemia is the result of decreased plasma volume, often due to acute dehydration from vomiting, diarrhea, or insufficient fluid intake. This concentrates existing red blood cells, artificially raising the Hct percentage.
Absolute polycythemia involves an actual increase in the total number of red blood cells. The most common form is secondary polycythemia, where the body produces more red blood cells in response to chronic low oxygen levels (tissue hypoxia).
Conditions causing chronic hypoxia include:
- Chronic obstructive pulmonary disease (COPD)
- Severe sleep apnea
- Congenital heart diseases
- Living at high altitudes
In these cases, the kidneys release erythropoietin (EPO), signaling the bone marrow to increase red blood cell production as compensation. Primary polycythemia, such as Polycythemia Vera, is a rare blood cancer where the bone marrow overproduces red blood cells independent of oxygen needs.
Clinical Strategies for Reduction
When Hct and Hgb levels are high enough to pose a health risk, medical professionals often turn to therapeutic phlebotomy as the standard treatment. This medically supervised blood draw, similar to donating blood, is the quickest way to reduce blood viscosity. The immediate removal of a specific volume of whole blood, typically between 450 to 500 milliliters, directly lowers the concentration of red blood cells.
The primary goal of therapeutic phlebotomy is to reduce the Hct to a target level, often below 45% for men and slightly lower for women, to mitigate the risk of thrombosis or blood clot formation. The frequency of phlebotomy sessions is highly individualized, ranging from daily in acute settings to monthly or quarterly for maintenance, determined by follow-up blood test results.
Repeated phlebotomy also works by inducing a state of mild iron deficiency, which is a secondary mechanism for limiting red blood cell production. Since iron is an essential component of hemoglobin, depleting iron stores naturally slows the bone marrow’s ability to create new red blood cells. In certain cases, particularly for managing Polycythemia Vera, physicians may prescribe cytoreductive agents like hydroxyurea. These medications suppress the production of blood cells in the bone marrow, but they are reserved for specific diagnosed conditions and are not a first-line therapy for most cases of elevated Hct.
Lifestyle and Nutritional Adjustments
Making lifestyle changes can significantly influence Hct and Hgb levels, especially for managing secondary and relative polycythemia. The fastest way to address elevated Hct due to hemoconcentration is ensuring adequate fluid intake. Proper hydration increases plasma volume, effectively diluting the concentration of red blood cells and immediately lowering the Hct percentage.
Dietary adjustments play a long-term role by modulating the body’s iron status, which is necessary for hemoglobin production. It is beneficial to adopt an iron-conscious diet, focusing on limiting iron-rich foods like red meat and iron-fortified cereals. Individuals should avoid taking iron supplements unless specifically instructed by a physician.
A nutritional consideration is the timing of vitamin C intake, as this vitamin enhances the absorption of non-heme iron from plant sources. Avoiding high-dose vitamin C supplements near mealtimes can help limit the amount of dietary iron absorbed by the body. Addressing environmental and health factors that cause chronic low oxygen is also a powerful adjustment.
If high Hct results from a chronic condition like obstructive sleep apnea, consulting a specialist to manage the disorder is necessary. Improving nocturnal oxygen saturation will reduce the body’s drive to produce excess red blood cells. Similarly, individuals living at very high altitudes who experience problematic elevations may need to adjust their environment or spend time at lower elevations. Avoiding smoking is essential, as carbon monoxide inhalation forces the body to create more red blood cells to compensate for reduced oxygen-carrying capacity.