What is fasting?

• Fasting is a common type of preparation required for blood tests, according to the National Library of Medicine (NLM) and the National Institutes of Health (NIH). It requires a patient to go without all or certain foods for six to 12 hours. Certain tests require patients to increase or decrease the amount of liquids consumed for 10 to 12 hours prior to the test. Patients may also be advised to avoid certain foods, drinks or medications. Certain behaviors, such as smoking, excessive exercise, dehydration or overeating, may also alter some results. Patients may be told to avoid these activities before certain tests. (Reference 1)
  
  Among the blood tests that require fasting are glucose tolerance and fasting blood glucose tests and complete lipid profiles.
  
  

Fasting Instructions

• Health care providers instruct their patients on how to prepare for the specific blood tests they are having. It is important for patients to listen to and follow these directions in order to ensure the accuracy of their test results. If they do not, patients must alert the lab technician drawing their blood. An explanation of how and why they deviated from their instructions must be given so that a physician can correctly interpret or discount the test results. If there is any confusion about the correct procedure for fasting before a blood test it is essential that patients ask their health care provider for clarification. Likewise, if no instructions are given, patients should double-check that no fasting is required.
  
  

Avoid Confusion

• The federal government has taken steps to help patients remember the correct fasting procedure prior to any blood test. The Centers for Medicare and Medicaid Services (CMS) regulates all non-research-related laboratory testing performed on humans in the US through the Clinical Laboratory Improvement Amendments (CLIA), according to the Department of Health and Human Services. Under the CLIA, a written copy of instructions on fasting or other measures to be followed prior to any moderate or complex blood test must be provided to all patients undergoing such tests.