Table 4

Example of specimens taken during a controlled fast

SpecimenTestBaseline samplePostprandial sampleSamples at regular intervalsEnd of fast samplesPost end of fast samples
BloodBedside glucose
(1 hourly)
Lab glucose and lactate
Free fatty acids
Growth hormone
Amino acids
Liver function tests
Ammonia and TCO2
Carnitine and acylcarnitine
UrineAmino acids and organic acids
Collect aliquots of all urine passed from the beginning of the fast and the first and second urines after the end of the fast. Label carefully with the time and store separately in fridge so that the end of fast specimens can be identified and analysed.
  • Urine amino acids: helpful in diagnosing aminoacidopathies.

  • Postprandial samples: samples taken 1–2 hours postcommencement of the fast. These samples are physiological postprandial samples as the fast commences after the patient is given a meal.

  • Post end of fast samples: samples taken after termination of controlled fast.