Determination of reference values for glucose tolerance, insulin tolerance, and insulin sensitivity tests in clinically normal cats

Objective-To determine reference values and test variability for glucose to lerance tests (GTT), insulin tolerance tests (ITT), and insulin sensitivity tests (IST) in cats, Animals-32 clinically normal cats. Procedure-GTT, ITT, and IST were performed on consecutive days. Tolerance i ntervals tie, reference values) were calculated as means +/- 2.397 SD for p lasma glucose and insulin concentrations, half-life of glucose (T-1/2glucos e), rate constants for glucose disappearance (K-glucose and K-itt), and ins ulin sensitivity index (S-l). Tests were repeated after 6 weeks in 8 cats t o determine test variability. Results-Reference values for T-1/2glucose, K-glucose, and fasting plasma gl ucose and insulin concentrations during GTT were 45 to 74 minutes, 0.93 to 1.54 %/min, 37 to 104 mg/dl, and 2.8 to 20.6 muU/ml, respectively. Mean val ues did not differ between the 2 tests. Coefficients of variation for T-1/2 glucose, K-glucose, and fasting plasma glucose and insulin concentrations w ere 20, 20, 11, and 23%, respectively. Reference values for K-itt were 1.14 to 7.3%/min, and for S-l were 0.57 to 10.99 x 10(-4) min/muU/ml. Mean valu es did not differ between the 2 tests performed 6 weeks apart, Coefficients of variation for K-itt and S-l were 60 and 47%, respectively. Conclusions and Clinical Relevance-GTT, ITT, and IST can be performed in ca ts, using standard protocols. Knowledge of reference values and test variab ility will enable researchers to better interpret test results for assessme nt of glucose tolerance, pancreatic beta -cell function, and insulin sensit ivity in cats.