High blood viscosity is medically called hyperviscosity. Middle-aged and elderly people are prone to it, and it can be diagnosed by blood rheology. The main factors affecting blood viscosity are: the first one is age, which tends to increase with age; another one is the cellular problems, such as blood cell factors, such as too many blood cells, size and shape, abnormal function, especially platelet function, may affect the blood viscosity; another one is the blood coagulation system problems, such as increased fibrin content, especially fibrinogen immunoglobulin. In addition, patients with hypertension, hyperlipidemia and diabetes tend to have increased blood viscosity; another condition is the vascular factors, such as the length and diameter of the blood vessels and the smoothness of the inner membrane, which may also affect the blood viscosity; other causes, such as long-term smoking and staying up late, may also lead to increased blood viscosity.