Determination of insulin-like growth factor 1 in dogs using a commercially available immunoradiometric assay1)

The objective of the present study was to characterize a commercially available immunoradiometric assay (IRMA) intended for the determination of human insulin-like growth factor 1 (IGF-1) when used to determine IGF-1 in canine plasma samples. The assay was evaluated by assessment of the precision, accuracy, and detection limit, and by comparing the IGF-1 values observed in healthy dogs and in dogs with acromegaly and hereditary pituitary dwarfism to values reported in the literature. Since extraction of IGF-1 from its binding proteins is essential for reliable test results, the efficiency of the extraction method used in the assay was also examined. The main conclusions can be summarized as follows: The commercially available IRMA method offers a precise determination of the IGF-1 concentration in canine plasma samples with IGF-1 values directly comparable to those obtained by others. The assay accuracy was confirmed for normal dogs by parallelity between IGF-1 concentrations and plasma dilutions, whereas plasma from acromegalic dogs could not fullful parallelity. The detection limit was below the IGF-1 concentrations observed in dogs with hereditary pituitary dwarfism. In plasma samples with low or normal IGF-1 levels, the assay's extraction efficiency was comparable to that found using other extraction methods. In samples with IGF-1 concentrations above usual physiological levels, the extraction efficiency decreased unexplainably. However, this decrease in extraction efficiency seems to be of only minor importance when the measurements are used in the diagnosis of canine acromegaly.