Inter- and intraindividual variability of the response to intravenous glucose tolerance testing in cats

To evaluate inter- and intraindividual variation in results of the intravenous glucose tolerance test in cats.

19 healthy specific-pathogen-free-derived cats were allotted to group A (n = 13), which was accustomed, and group B (n = 6), which was unaccustomed to having blood drawn.

Blood samples were collected for glucose and insulin assays before and 5, 10, 15, 30, 45 and 60 minutes after i.v. administration of 500 mg of dextrose/kg of body weight. Glucose half-life (t1/2) and disappearance co-efficient (K), and the acute-phase insulin response (Ins0-10) were calculated. Inter- and intraindividual variability was assessed by calculating the coefficient of variation for test variables.

Comparing the 2 tests, there were no significant differences in glucose and insulin concentrations prior to dextrose administration or in t1/2, K, or Ins0-10. However, compared with group-A cats, cats in group B had significantly (P < 0.05) longer t1/7 and lower K and Ins0-10 values, which was attributed to increased stress in these cats. Overall, the interindividual variability was 62.8% for K, 54.6% for t1/2, and 76.0% for Ins0-10. Mean intraindividual variability was 32.0 (range, 0.1 to 72.0)% for K and t1/2, and 45.8 (range, 4.0 to 179.5)% for Ins0-10. There was only a moderate correlation in results between the 2 tests (rs = 0.59 for t1/2 and K, rs = 0.58 for Ins0-10).

The variability in results of intravenous glucose tolerance tests in cats suggests caution is necessary in interpreting results of a single test in individuals.