Elevated 25-hydroxy and normal 1,25-dihydroxy cholecalciferol serum concentrations in a successfully-treated case of vitamin D₃ toxicosis in a dog

A 4-y old, 27 kg spayed female German Shepherd dog was observed to ingest one 1-oz package of a rodenticide containing cholecalciferol. An initial serum calcium concentration of 15.7 mg/dl was successfully reduced to normal during 10 d using calcitonin and prednisolone. During that time, the serum 25-hydroxy and 1,25-hydroxy cholecalciferol concentrations ranged from 637 to 315 ng/ml (normal 32 ± 6 ng/ml) and 64 to 29 pg/ml (normal 34 ± 19 pg/ml), respectively. Serum mid-molecule parathyroid hormone concentrations (76 to 97 pcmol/L) were within the normal range (85-140 pcmol/L). These data indicate that hypercalcemia seen in dogs following field exposures to cholecalciferol-containing rodenticides may be associated with elevated 25-hydroxy rather than 1,25-dihydroxy cholecalciferol. Consequently, serum 25-hydroxy cholecalciferol concentrations may be the most conclusive method for diagnosing hypervitaminosis D₃ toxicosis in the live dog.