Cholesterol is different from most tests in that it is not always used to diagnose or monitor a disease but is used to estimate risk of developing a disease — specifically heart disease. Because high blood cholesterol has been associated with hardening of the arteries, heart disease and a raised risk of death from heart attacks, cholesterol testing is considered a routine part of preventive health care.

Cholesterol testing is recommended when you have established heart disease (angina, heart attack), or if there is a family history of high cholesterol, or of heart disease at an early age; if you are over 35 years of age and have risk factors which put you at an increased chance of developing heart disease, such as diabetes, high blood pressure, or you are a smoker. In addition, cholesterol testing is performed if you are following a recommended diet or taking drugs to lower your cholesterol level, to monitor your response to treatment. Total cholesterol may be measured alone or in combination with other tests including HDL, LDL, and triglycerides — often called a lipid profile.

The cholesterol level measured in your blood will be considered along with other risk factors for heart disease (high blood pressure, smoking etc.) when assessing your overall risk of developing heart disease. This overall assessment is what will used to decide whether or not you require further treatment in the form of dietary changes or drugs to lower your cholesterol level.
If you are taking treatment to lower your cholesterol, the target is to get your total cholesterol to a value less than 5 mmol/L, with a fall of around 20-25%.

Cholesterol should be measured when a person is healthy. Blood cholesterol is temporarily low during acute illness, immediately following a heart attack, or during stress (like from surgery or an accident). You should wait at least 6 weeks after any illness to have cholesterol measured.

There is some debate about whether very low cholesterol is bad. Low cholesterol is often seen when there is an existing problem like malnutrition, liver disease, or cancer. However there is no evidence that low cholesterol causes any of these problems.

Cholesterol is high during pregnancy. Women should wait at least six weeks after the baby is born to have cholesterol measured.

Some drugs that are known to increase cholesterol levels include oral corticosteroids, beta blockers, oral contraceptives, thiazide diuretics, oral retinoids and phenytoin.