Sleep apnea can cause high hematocrit levels. Obstructive Sleep Apnea (OSA) is a disorder where the upper airway repeatedly closes or narrows during sleep, leading to frequent interruptions in breathing and drops in blood oxygen saturation. Hematocrit measures the percentage of total blood volume made up of red blood cells. An elevated hematocrit, often termed secondary polycythemia, significantly alters blood composition and increases cardiovascular risk.
Understanding High Hematocrit and Associated Risks
High hematocrit means the proportion of red blood cells in the blood is above the normal range, a condition known as erythrocytosis or secondary polycythemia. Red blood cells are essential for transporting oxygen throughout the body, but an excessive number increases the blood’s thickness, a property called viscosity. This elevated viscosity forces the heart to work harder to pump the thicker blood through the circulatory system, especially small capillaries.
The primary danger of high hematocrit stems from this increased viscosity, which significantly raises the risk of blood clots. Thicker blood flows less smoothly and is more prone to forming blockages within blood vessels. These clots can lead to serious events such as a stroke or a heart attack. Patients with high hematocrit may also experience symptoms like headaches, dizziness, blurred vision, and general fatigue due to impaired circulation.
The Physiological Mechanism Linking Apnea and Hematocrit
The development of high hematocrit in sleep apnea patients is a direct result of the body’s attempt to compensate for chronic low oxygen levels. During apneic events, the repeated pauses in breathing cause the oxygen saturation in the blood to drop dramatically, a state known as intermittent hypoxia. The body interprets this recurring nocturnal oxygen shortage as a need for more oxygen carriers.
This compensatory mechanism is orchestrated by the kidneys, which function as the primary oxygen sensors in the body. In response to chronic hypoxia, the kidney tissue dramatically increases the production and release of the hormone Erythropoietin (EPO). EPO is a powerful signaling molecule that travels through the bloodstream to the bone marrow, the body’s blood cell factory.
Once in the bone marrow, EPO stimulates erythropoiesis, accelerating the rate at which red blood cells are produced. This overproduction leads to the elevated red blood cell count and the resulting high hematocrit. Studies show a correlation between the severity of Obstructive Sleep Apnea (OSA), particularly the time spent at low oxygen saturation, and higher hematocrit values. This condition is more prevalent in patients with severe OSA.
Resolution of High Hematocrit Through Sleep Apnea Treatment
Fortunately, the secondary polycythemia caused by sleep apnea is typically reversible once the underlying breathing disorder is effectively managed. The standard and most effective treatment for Obstructive Sleep Apnea is Continuous Positive Airway Pressure (CPAP) therapy. CPAP devices deliver pressurized air through a mask, which keeps the upper airway open during sleep, thus eliminating the apneic events and the associated intermittent hypoxia.
By stopping the nocturnal oxygen drops, CPAP removes the chronic hypoxic signal that drives the compensatory mechanism. With normalized oxygen levels, the kidneys reduce their production of the EPO hormone over time. This decrease in EPO then slows down the rate of red blood cell production in the bone marrow.
Clinical studies have demonstrated that using CPAP therapy reduces hematocrit levels in patients with OSA. This reduction can occur relatively quickly, with some research showing a decrease after the very first night of treatment. Over several months of consistent CPAP use, the hematocrit gradually returns toward the normal range as the body corrects the red blood cell overproduction. Continued monitoring of blood counts by a physician is important to ensure the treatment successfully normalizes the hematocrit levels.