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Glucose tolerance test

ISSN 2398-2950

Contributor(s) :

Synonym(s): oral glucose tolerance, intravenous glucose tolerance


Test not used in clinical practice (only research settings).



In combination


Source of test material

Quantity of test material

  • 0.5 ml whole blood, (or a drop of blood if glucometer available Glucometer ).

Sample collection technique

  • Fast animal for 12 hours prior to testing.
  • Baseline blood into fluoride oxalate (0.5 ml), labelling sample with time and owner's name.
    Insert in-dwelling intravenous catheter to reduce stress of sampling. Flush with heparinized saline and cap in normal manner.

Step 2

  • Intravenous method: slow intravenous injection over 30 s of 500 mg glucose/kg bodyweight as 50% solution.
    Not advisable to use catheter for glucose injection (use another site), as may   →   spurious results.
  • Oral method: 25% solution administered by mouth at 2 g/kg bodyweight. Best administered by stomach tube.
    May stimulate vomiting.

Step 3

  • Take further samples into fluoride oxalate following glucose administration at 5, 10, 15, 30, 45 and 60 min.
    Results markedly affected by stress at sampling, inappetence and exercise.

Quality control


  • Label sequential samples with care. (Easy to mix up.)

Sample storage

  • Store samples in refrigerator prior to despatch.

Sample transport

  • Standard mail.



Technique intrinsic limitations

  • There is always a risk of life-threatening hypoglycemia Hypoglycemia, developing on glucose challenge in animals with insulinoma.
  • Sudden rises in plasma glucose stimulate massive insulin secretion.

Result Data

Normal (reference) values

  • In normal animal, plasma glucose rises immediately and then rapidly falls off to return to normal values usually within 2-3 hours.
  • Glucose half-life 16-38 mins.
  • K value 2.83 +/- 0.96.

Abnormal values

  • Initially diabetic cats may have a reduced first phase of insulin secretion (2-15 min) followed by a delayed, exaggerated insulin response.
  • Glucose intolerance, ie diabetes mellitus Pheochromocytomas, hyperadrenocorticism   Hyperadrenocorticism  second phase of insulin secretion is lost   →   glucose levels stay higher longer.
  • Islet cell tumor, lower maximum plasma glucose levels and more rapid return to pre-glucose levels.

Errors and artifacts

  • Stress at sampling may result in longer half-life of glucose.

Further Reading


Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Feldhahn J R et al (1999) The effect of interday variation and a short term stressor on insulin sensitivity in clinically normal cats. J Fel Med Surg (4), 233-240.
  • Martin G J W et al (1999) Food intake and blood glucose in normal and diabetic cats fed ad libitum. J Fel Med Surg (4), 241-251.
  • Link K R J & Rand J S (1998) Reference values for glucose tolerance and glucose tolerance status in cats. JAVMA 213, 492-496.
  • Link K R J, Rand J S & Hendrikz J K (1997) Evaluation of a simplified intravenous glucose tolerance test and a reflective glucose meter for use in cats. Vet Rec 140, 253-256.
  • Sparkes A H, Adams D T, Cripps P J et al(1996) Inter and intraindividual variability in the reponse to intravenous glucose tolerance testing in cats. Am J Vet Res 57, 1294-1298.
  • Nelson R W, Himsel C A, Feldman E C & Bottoms G D (1990) Glucose tolerance and insulin response in normal weight and obese cats. Am J Vet Res 51, 1357-1362.

Other sources of information

  • Norton F (1985) The normal feline intravenous glucose tolerance test curve and concurrent insulin response curve. Proc 3rd Ann Med Forum, San Diego.