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Name: Rodolfo
Status: Other
Grade:  Other
Location: N/A
Country: Puerto Rico
Date: February 2008

Why patients are requesting not to eat before a common blood draw?

Some of the tests are affected by metabolized food products. For example, after you eat and your food is digested, carbohydrates are broken down into glucose. this will raise the glucose level. If the doctor is testing you for diabetes, it will be difficult to know if the elevated glucose is due to true elevation in glucose or because it is after a meal. Other tests that might be affected are cholesterol, and triglycerides. So the tests should be done before you eat in the morning.


Some blood tests require a "fasting" period. Others do not. The classic example is "blood sugar". If the subject has a high sugar meal before the blood is drawn, a transient high sugar level may result. This might be interpretted as a diabetic response, when in fact it is a transient sugar "high". Other food intakes likewise may result in a false positive or negative results. For this reason the general rule is a "fasting" diet.

Vince Calder

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