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Glucose tolerance test

ISSN 2398-2950

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

Overview

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

Uses

Alone

In combination

Sampling

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

Precautions

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

Sample storage

  • Store samples in refrigerator prior to despatch.

Sample transport

  • Standard mail.

Tests

Availability

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

Publications

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.