Abstract BackgroundInsulin‐like growth factor‐I (IGF‐I) is used to screen for acromegaly in diabetic cats. In humans, most circulating IGF‐I forms ternary complexes (TC) with IGF‐binding protein (IGFBP‐3) and an acid‐labile subunit. Compared to humans, the amount of TC in cats is more variable. Insulin‐like growth factor‐I concentrations are reported to increase during insulin treatment, more rapidly in cats achieving remission.ObjectivesTo investigate (i) factors associated with circulating IGF‐I concentrations, including IGFBP‐profiles (ii) effect of insulin treatment on IGF‐I concentrations and (iii) IGF‐I as prognostic marker of diabetes mellitus remission.AnimalsThirty‐one privately owned diabetic cats of which 24 were followed 1 year, and 13 healthy cats.MethodsProspective study. Serum insulin, IGF‐I, glucose, and fructosamine concentrations were measured. IGF‐binding forms were determined by chromatography in 14 diabetic and 13 healthy cats; and IGF‐I, IGF‐II, IGFBP‐3, and IGFBP‐5 by mass spectrometry in 3 cats achieving remission.ResultsInsulin‐like growth factor‐I median (interquartile range) before start of insulin treatment was 300 (160‐556) ng/mL. Insulin‐like growth factor‐I was positively associated with TC (P