The Difference Between Nonfasting & Fasting Cholesterol Tests

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The amount of cholesterol in your blood is directly correlated with your risk of developing heart disease, the leading cause of death in the United States. Cholesterol tests involve drawing a blood sample from your arm to measure the level of cholesterol components in your blood. The American Heart Association recommends that adults over the age of 20 have their cholesterol checked every five years.

Fasting Versus Non-fasting

A fasting cholesterol test is one that is performed after a specified period of time during which a person has not eaten or drunk anything with the exception of pure water. A non-fasting cholesterol test, sometimes referred to as a random cholesterol test, measures your cholesterol level without any restrictions on your dietary intake. Some cholesterol tests require you to fast, while others are not affected by food intake.

Types of Cholesterol Tests

A total cholesterol test involves one measurement, which combines LDL, or bad, cholesterol and HDL, or good, cholesterol. It is not necessary to fast before a total cholesterol test because the value does not change significantly after eating, according to the Harvard Health Publications. A lipid profile, which includes values for total cholesterol, as well as individual values for LDL cholesterol, HDL cholesterol and triglycerides, another lipid in the blood, requires you to fast.

Reason to Fast

LDL levels cannot be measured from the blood directly. Instead, a mathematical equation called the Friedewald equation, is used to calculate LDL levels using values for total cholesterol, HDL cholesterol and triglycerides. The equation divides your triglyceride level by 5 and then subtracts this value as well as your HDL value from your total cholesterol. The result is your LDL level. When you eat, your triglyceride levels rise 20 to 30 percent, according to the Harvard Health Publications. Because this increase in triglycerides affects the outcome of the Friedewald equation significantly, it is necessary to fast before a lipid profile, individual LDL test or triglyceride screening.

Length of Fast

According to the Health Services at Columbia, fat and cholesterol components are usually only measurable for approximately 10 hours after a meal. Because of this, most physicians recommend fasting for a period of at least 12 hours before a fasting cholesterol test. Alcohol can increase your triglyceride levels significantly, so abstain from alcohol for at least 24 hours before a fasting cholesterol test.

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