Serum insulin-like growth factor-1 concentrations in healthy cats before and after weight gain and weight loss

Background: Measurement of serum concentrations of insulin-like growth factor (IGF)-1 is used to diagnose acromegaly in cats. Hypothesis: Changes of body weight do not affect serum concentrations of IGF-1 in cats. Animals: Ten healthy purpose-bred cats. Methods: Prospective study. In lean cats, food availability was stepwise increased during the first week and given ad libitum for a total of 40 weeks to increase their body weight. From week 41 to week 60, food access was limited to reach a weight loss of 1% to 2% each week. Measurement of IGF-1 was performed at week 0, 16, 40, and 60. Insulin-like growth factor-1 was measured by radioimmunoassay. Body weight and IGF-1 were compared among the 4 time points. Results: Body weight increased by 44% from week 0 (4.5 ± 0.4 kg) to week 40 (6.5 ± 1.2 kg) (P <.001) and decreased by 25% from week 40 to week 60 (4.9 ± 0.7 kg) (P <.001). Serum IGF-1 concentrations did not differ during the study period (week 0, 16, 40, 60: 500 ± 188, 479 ± 247, 470 ± 184, 435 ± 154 ng/mL, respectively; P =.38). Correlations with body weight were not observed. Conclusions and Clinical Importance: Insulin-like growth factor-1 might not be influenced by changes of body weight in healthy cats, possibly suggesting that the latter is unimportant when interpreting IGF-1 results in this species.