The sensation of “concentrated blood” refers to a condition known medically as high blood viscosity or polycythemia, where the blood is thicker or more resistant to flow than normal. This increased thickness is often indirectly measured by the hematocrit level, which represents the percentage of the total blood volume occupied by red blood cells. When the proportion of solid components, particularly red blood cells, increases relative to the fluid component (plasma), the blood becomes physically harder to move through the circulatory system.
Understanding Blood Concentration
Blood is a complex fluid composed of plasma, which is mostly water, and various solid components, including red cells, white cells, and platelets. The hematocrit (Hct) is the standard measurement used to quantify this concentration, representing the volume percentage of red blood cells in the blood sample. For adult males, a normal hematocrit range is typically between 41% and 50%, while for adult females, it is between 36% and 48%. When this percentage rises above the normal range, the increased cellular volume raises the blood’s resistance to flow, which forces the heart to work harder to maintain circulation.
Primary Causes of High Blood Concentration
The causes of high blood concentration fall into two main categories: relative polycythemia, which is temporary and due to fluid loss, and absolute polycythemia, which involves an actual increase in red blood cell mass. Dehydration is the most common cause of relative polycythemia, occurring when the body loses plasma volume from insufficient water intake or conditions like severe vomiting or diarrhea. When plasma volume decreases, the remaining red blood cells are more densely packed, artificially inflating the hematocrit reading.
Absolute polycythemia (erythrocytosis) is a persistent issue caused by the overproduction of red blood cells. A primary example is Polycythemia Vera (PV), a bone marrow disorder where the body produces an excessive number of red cells, often alongside increased white cells and platelets. This condition is linked to a genetic mutation, most commonly in the JAK2 gene, which causes bone marrow cells to grow independently of normal regulatory signals.
Secondary causes of absolute polycythemia occur when the body produces extra red blood cells in response to chronic low oxygen levels (hypoxia). Conditions like severe lung disease (e.g., chronic obstructive pulmonary disease), heart disease, or living at very high altitudes trigger the release of erythropoietin (EPO), stimulating red blood cell production. Smoking is another significant secondary cause because carbon monoxide reduces the blood’s ability to carry oxygen, prompting the body to compensate by making more red blood cells.
Health Impacts and Associated Risks
The primary danger associated with concentrated blood is the increased resistance to flow, which significantly elevates the risk of forming blood clots (thrombosis). This slow flow facilitates the formation of blockages within blood vessels, which can lead to life-threatening events such as stroke, heart attack, or pulmonary embolism.
The heart must pump harder to circulate the thicker blood, increasing the cardiovascular workload and potentially leading to elevated blood pressure. This chronic strain can contribute to heart failure and damage the inner lining of the blood vessels. Common symptoms related to sluggish circulation include headaches, dizziness, fatigue, and blurred vision. Some individuals may also experience flushing or redness of the skin and generalized itchiness, especially after a warm bath or shower.
Diagnosis and Management Strategies
Diagnosis of high blood concentration typically begins with a Complete Blood Count (CBC), which measures hematocrit and hemoglobin levels. If the hematocrit is elevated, further testing is required to distinguish between temporary fluid loss and actual red blood cell overproduction. These additional tests may include measuring erythropoietin (EPO) levels and screening for the JAK2 gene mutation associated with Polycythemia Vera.
For relative polycythemia caused by dehydration, the most effective management is restoring the body’s fluid balance through increased intake of water and electrolytes. This dilutes the blood plasma, returning the hematocrit to a normal range.
For absolute polycythemia, especially Polycythemia Vera, the primary treatment is therapeutic phlebotomy—a controlled removal of blood to physically reduce the red blood cell count. The goal of phlebotomy is to bring the hematocrit down to a target level (often below 45% for men and 42% for women) to mitigate clotting risk. Patients may also be prescribed low-dose aspirin to further reduce thrombosis risk, and sometimes myelosuppressive medications, such as hydroxyurea, to suppress the overproduction of blood cells in the bone marrow.