Why do doctors monitor the concentrations of LDL and HDL in a patients blood?

Doctors might want to monitor the concentrations of LDL and HDL because if you have too much LDL and low HDL then you can get plaque in your arteries, which can lead to getting cardiovascular disease. Cardiovascular disease is a serious heart condition that can cause a patient to be at a high risk of getting a heart attack, stroke, and high blood pressure. On the other hand having your HDL higher than your LDL is better because it helps prevent the development of Plaque in your arteries and decreases the risk of getting heart disease and cardiovascular disease. Since there is no symptoms or warning signs to having a high cholesterol  it is important for doctors to monitor the concentrations of LDL and HDL in a patient's blood often to make sure that their overall health is not at risk of any life threatening conditions.

References: "High Cholesterol." Mayo Clinic. Mayo Foundation for Medical Education and Research, 09 Feb. 2016. Web. 21 Apr. 2017.