I have raised plasma viscosity in blood is it harmfull and does it cause any problems?

Yes, it may : Depending on how high is your serum viscosity level and off course- what the cause of the elevation of serum viscosity- some serious problem can happen. When the serum viscosity is above certain level -above 4- you could have symptoms like headaches, chest pain, shortness of breath, stroke-like symptoms etc. The higher the level the higher your risk is. Discuss in detail with your doctor.