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Fasting Instructions

If you have a Urea Breath Test for Helicobacter pylori ordered, refer to Patient Instruction Sheet CH3067.

For ALL other fasting tests:

  • Have NOTHING to eat, chew (including gum or candy) or drink (except water) for the period specified in the chart below, for the test you are having performed.
  • Prescription drugs are permitted, unless specific instructions were provided directing you otherwise.

Tests which require fasting:

 Test Length of fast 
 Acylcarnitine Profile  Minimum 4 hours, or just prior to next feed for newborns
 Amino Acids  Minimum 4 hours, or just prior to next feed for newborns (unless requested as
 nonfasted by physician)
 Beta-Carotene  Minimum 10 hours with no alcohol or nutritional supplements within 24 hours
 Beta-Hydroxybutyrate  Minimum 8 hours (reference interval applied to 8-15 hours fasted)
 Nonfasted also acceptable (different reference interval)
 Bile Acids  8 hours
 Carnitine, Total and Free  Minimum 4 hours, or just prior to next feed for newborns
 Cryofibrinogen  Fasting specimen preferred
 Cryoglobulin  Fasting specimen preferred
 CTx  Overnight fast preferred
 7-Dehydrocholesterol  Minimum 4 hours, or just prior to next feed for newborns
 Electrophoresis,
 Lipoprotein
 Minimum 12 hours
 Fatty Acids, Free  12 hours
 Fatty Acids, Very Long
 Chain
 Minimum 4 hours, or just prior to next feed for newborns;
 avoid peanut containing foods for 24 hours prior to collection
 Glucagon  Overnight
 Glucose  Minimum 8 hours, but not more than 16 hours
 Glucose Tolerance  Minimum 8 hours, but not more than 16 hours
 Homocysteine  Overnight fast preferred
 Homocysteine (Pediatric),
 Total
 Minimum 4 hours, or just prior to next feed for newborns
 Insulin  8 hours
 Lactose tolerance  Minimum 8 hours
 Metanephrines - Plasma   Minimum 4 hours, including no smoking tobacco
 3-Methylglutaconic and
 3-Methylglutaric Acids
 Minimum 4 hours
 Methylmalonic Acid  Minimum 4 hours, or just prior to next feed for newborns
 Pancreatic Polypeptide  Overnight preferred
 Pipecolic Acid  Minimum 4 hours, or just prior to next feed for newborns
 Plasma Metanephrines  Minimum 4 hours, including no smoking tobacco
 Proinsulin  Overnight fast
 S-Adenosylmethionine and
 S-Adenosylhomocysteine
 Minimum 4 hours, or just prior to next feed for newborns
 Urea Breath Test for
 Helicobacter pylori
 See Patient Instruction Sheet CH3067.
 Vitamin A  Minimum 10 hours. No alcohol or nutritional supplements within 24 hours.
 Vitamin E  Minimum 10 hours. No alcohol, foods or nutritional supplements containing
 Vitamin E within 24 hours.
 Xylose Tolerance  10 hours (9 hours if diabetic)