What is polycythaemia?

Explanation

### Step-by-Step Solution:

1. **Definition of Polycythemia**: Polycythemia is a medical condition characterized by an increased number of red blood cells (RBCs) in the bloodstream. It is also referred to as erythrocytosis.

2. **Causes of Polycythemia**: The increase in RBC count can occur due to abnormal production of red blood cells. This can be caused by various factors, including genetic mutations, chronic hypoxia, or other underlying health conditions.

3. **Effects on Blood Properties**: As the number of RBCs increases, the blood becomes thicker and stickier. This change in blood viscosity can lead to complications in blood flow.

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