VET Talks is a project by the IVSA Standing Committee on Veterinary Education (SCoVE).

This VET Talks is by Dr Sheena Warman, BSc, BVMS, DSAM, DipECVIM-CA, SFHEA, MRCVS, Senior Clinical Fellow in Small Animal Medicine, University of Bristol (UK)

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The Diagnosis Of Canine Diabetes Insipidus

Diabetes insipidus is a hormonal condition characterized by the inability of the kidneys to concentrate urine. Antidiuretic hormone (ADH) operates on the kidney to regulate the amount of water excreted in the urine. When the body requires water, ADH levels rise. As a result, the kidney retains the water and prevents it from being passed through the urine; Conversely, when the body has excess water, the kidney permits surplus water to pass into the urine.

When antidiuretic hormone (ADH) is supplied directly to the pet, the vasopressin test determines the kidneys’ ability to concentrate urine. In addition, the value of plasma osmolality — this value indicates the amount of water in the blood. When the pet is denied water, the modified water deprivation test assesses the body’s ability to produce urine.

A veterinarian can diagnose the condition of primary polydipsia or psychogenic thirst if a pet can concentrate urine while dehydrated. The brain produces insufficient ADH hormone; without ADH, the kidneys lose a significant amount of water through the urine, and the pet must consume excessive amounts of water to compensate. Nephrogenic diabetes insipidus is the most likely diagnosis because the brain produces adequate amounts of the hormone in this situation, but the kidney cannot respond.

A pet with diabetes insipidus will have a high plasma osmolality. This is because, in the absence of ADH, the kidneys would lose vast amounts of water, leaving the body dehydrated. Conversely, a pet suffering from primary polydipsia/psychogenic thirst will typically have a low plasma osmolality due to the amount of water consumed.

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