Secondary erythrocytosis is a condition where the body produces an abnormally high number of red blood cells. These cells, also known as erythrocytes, carry oxygen throughout the body. When their count becomes too high, it leads to a thickening of the blood, which can impede its flow. This condition is a response to an underlying health issue rather than a primary disorder of the blood-forming system.
Understanding Secondary Erythrocytosis
Secondary erythrocytosis involves the body increasing red blood cell production in response to a specific stimulus. The kidneys release a hormone called erythropoietin (EPO), which signals the bone marrow to produce more red blood cells. In secondary erythrocytosis, this process is stimulated by factors outside the bone marrow.
This condition differs from primary erythrocytosis, such as Polycythemia Vera (PV). In primary erythrocytosis, the bone marrow has a problem, often a genetic mutation, causing it to overproduce red blood cells independently. Conversely, secondary erythrocytosis is an acquired condition, developing in response to other health problems, and the bone marrow’s red blood cell production is still regulated by EPO, even if elevated.
Causes of Elevated Red Blood Cells
The increase in red blood cells in secondary erythrocytosis stems from the body’s attempt to compensate for insufficient oxygen delivery to tissues, or from an inappropriate increase in erythropoietin production.
Hypoxia-Related Causes
Chronic low oxygen levels, known as hypoxia, are a common trigger for secondary erythrocytosis, with conditions like chronic lung diseases (COPD, emphysema) and living at high altitudes being key factors. Severe sleep apnea, characterized by repeated pauses in breathing during sleep, also leads to intermittent drops in blood oxygen, stimulating erythropoietin release. Additionally, certain heart conditions can result in deoxygenated blood bypassing the lungs and entering systemic circulation, leading to chronic low oxygen. Heavy smoking is another factor, as carbon monoxide in cigarette smoke reduces hemoglobin’s oxygen-carrying capacity.
Kidney-Related Causes
The kidneys play a central role in red blood cell production by producing erythropoietin. Conditions affecting the kidneys can lead to increased red blood cell counts. Renal cysts and kidney tumors can inappropriately secrete erythropoietin, leading to an overproduction of red blood cells. Impaired blood flow to the kidneys can also cause local hypoxia within the kidney tissue, stimulating erythropoietin release even if overall body oxygen levels are normal. Kidney transplant rejection can also contribute to elevated red blood cell counts.
Other Causes
Beyond hypoxia and direct kidney issues, other factors can contribute to secondary erythrocytosis. Certain tumors located outside the kidney can produce and release erythropoietin. The use of exogenous hormones like androgen or anabolic steroids can also stimulate erythropoietin production. Some rare genetic disorders can also cause secondary erythrocytosis by affecting how the body senses oxygen or responds to erythropoietin.
Recognizing the Signs and Symptoms
The symptoms of secondary erythrocytosis arise from the increased thickness of the blood, known as hyperviscosity, which makes it harder for blood to flow through smaller vessels. This reduced blood flow can lead to a variety of general symptoms.
Common manifestations include headaches, dizziness, and fatigue. Individuals may experience shortness of breath, blurred vision, or a flushed, reddish appearance of the skin. Itching and ringing in the ears are also reported symptoms. The specific signs can also be linked to the underlying condition causing the erythrocytosis, such as a cough or snoring if sleep apnea is the cause.
Diagnosis and Management
Diagnosing secondary erythrocytosis begins with routine blood tests. A complete blood count (CBC) will reveal elevated levels of hemoglobin, hematocrit, and the red blood cell count.
Measuring erythropoietin (EPO) levels is a significant step, as these levels are usually high or within the normal range in secondary erythrocytosis, contrasting with the low levels seen in primary forms. To pinpoint the underlying cause, additional tests may be conducted, including oxygen saturation assessments, lung function tests, and sleep studies. Imaging of the kidneys and cardiac evaluations may also be performed to identify kidney issues or heart conditions.
The primary goal in managing secondary erythrocytosis is to identify and address the underlying condition responsible for the increased red blood cell production. For example, if smoking is the cause, cessation is advised, or oxygen therapy may be provided for hypoxia-related conditions like chronic lung disease. In some cases, surgical removal of erythropoietin-secreting tumors can resolve the condition. While treating the root cause is paramount, supportive treatments like therapeutic phlebotomy, which involves removing a quantity of blood, can reduce the red blood cell count and decrease blood viscosity, alleviating symptoms and preventing complications. It is important to consult a healthcare professional for an accurate diagnosis and a personalized treatment plan.