A person's cholesterol level is considered high if he has more than 240 milligrams of cholesterol per deciliter of blood, according to the National Heart, Lung, and Blood Institute. A cholesterol level of 200 to 230 milligrams per deciliter is considered borderline high and should be carefully monitored.
Factors that affect cholesterol levels include a person's diet, weight and level of physical activity, according to the National Heart, Lung, and Blood Institute. Being active and choosing nutritious foods can help naturally lower cholesterol levels.
Cholesterol levels should be tested via a blood test at least once every five years for all patients over age 20, states WebMD. This is true even if a patient currently has no symptoms of high cholesterol.