Cholesterol levels in the blood can fluctuate somewhat throughout a day, but not by much. The way we measure cholesterol in the blood is through a calculation that involves the use of triglycerides (fat) in the blood. If triglyceride levels are really high, they can interfere with an accurate calculation of the good and bad cholesterol levels. However, this is most often not a major problem. Some doctors
will still have people get blood work when fasting to avoid this problem, but with today's instruments, it is not that big of a deal.
The more important question you ask is the second one which is why cholesterol should be monitored. For good cholesterol monitoring, you should schedule an appointment with your primary care physicians. Cholesterol should be checked yearly in men over the age of 40 and women over the age of 50. There are some situations such as patients with a strong family history of heart disease where you would want it checked earlier. High bad cholesterol (called LDL) has been directly associated with coronary artery disease and blockages that can lead to heart attacks. Therefore, it is good to have your cholesterol checked regularly and make changes to your diet and lifestyle if it creeps up to dangerous levels. If these measures don't work, there are many great medications that can help lower cholesterol which helps prevent heart attacks. Please speak with your primary care physician