Abstract: Accurate insulin quantification is essential in veterinary endocrinology for diagnosing insulinoma and assessing insulin resistance in dogs. The gold standard, radioimmunoassay (RIA), offers high analytical precision but requires up to 48 hours for results, delaying clinical decisions. Faster methodologies could enhance diagnostic efficiency and patient management. This study validated a modified magnetic immunoassay (PMI) for canine insulin measurement by comparing its analytical performance with RIA and assessing its reliability for same-day results. Fifty-one dogs were categorized into two groups: 42 healthy dogs (normal insulin range: 6–32 µU/mL) and 9 dogs with confirmed insulinoma (insulin ≥70 µU/mL; blood glucose < 50 mg/dL). Serum samples were collected from clinical evaluations at the Hormonalle® Laboratory (São Paulo, Brazil). Insulin concentrations were determined using RIA (Millipore Sigma Human Insulin Kit, St. Louis, MO, USA) and PMI (Magnetic Immunoassay System, DiaSorin, Saluggia, Italy). For healthy dogs, mean insulin concentrations were 19.71 ± 6.13 µU/mL (RIA) and 18.64 ± 5.94 µU/mL (PMI; p = 0.47, r = 0.98). In insulinoma cases, RIA measured 99.76 ± 24.35 µU/mL and PMI 96.12 ± 23.5 µU/mL (p = 0.19, r = 0.94). No statistically significant differences were observed. PMI showed concordance with RIA while offering faster processing. Same-day results enhance clinical workflows and enable timely decisions, particularly for urgent cases such as insulinoma diagnosis. These advantages position PMI as a practical and reliable tool for routine endocrine assessments in veterinary practice.
