Fasting Instructions

Most patients are instructed to fast to prepare for a routine blood test. They are usually told to stop eating or drinking anything except water 8-12 hours before getting their blood test, particularly if they are to undergo testing for fasting blood sugar  (FBS) levels and/or lipid levels. Recommendations for fasting before blood exams were originally made to reduce variability and to achieve consistency in the patient’s metabolic state at the time of blood extraction. It is believed that food and beverages contain nutrients that are absorbed into the blood stream and could affect certain factors measured in the blood tests, such as your glucose or lipid (cholesterol and triglyceride) levels.

Many patients, however, have difficulty keeping their fasting state. Some are inclined to forget or even cheat, which may lead to postponing or repeating their tests. Poor patient compliance may also lead some people to avoid getting tested. Furthermore, some doctors also sympathize with their patients, whom they feel, are placed on unnecessary starvation.

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Several studies have recently suggested that patients may not be required to fast before getting some of their lab exams, particularly their lipid profiles. Of course, a fasting blood sugar (FBS) test requires at least an eight-hour fast, since the test wants to find out how much sugar is left in the blood even when a person has not eaten for several hours. But this is not the same for blood cholesterol exams. Researchers found that there is a minimal difference in the results of lipid profiles between the fasting state and the non-fasting state, which makes the obligatory fasting unnecessary for these tests.