Diagnosing Dehydration in Dogs

Source: PetWave, Updated on July 16, 2015

Initial Evaluation

When a veterinarian sees a dog that just “ain’t doing right” (called “ADR” in veterinary circles), he will take a full history and perform a thorough physical examination. He also typically will draw blood samples for a complete blood count and serum biochemistry profile, urine for a urinalysis and a fecal sample for parasite evaluation. Two inexpensive and easily performed tests involve assessing a blood sample to determine packed cell volume (PCV) and total plasma protein (TPP). These tests require only a few drops of blood each and can be done rapidly in a veterinary clinic. The results of blood, urine and fecal tests should provide valuable information about the dog’s overall health and the functional capabilities of its vital organs. They usually will identify the existence – but not the magnitude or degree – of dehydration if it is present. Increased PCV and TPP, together with abnormal levels of urine specific gravity, are suggestive of dehydration, although some dehydrated dogs can have normal values. It typically is not possible to identify dehydration until about 5% of a dog’s body weight in water is lost.

Diagnostic Procedures

Advanced diagnostic testing can be conducted based on the results of the initial database. These may include thoracic radiographs (chest X-rays), thoracic and abdominal ultrasound, urine culture, fecal culture, testing for ingestion of antifreeze (ethylene glycol), parvoviral testing, assessment of adrenal hormone production and function (adrenocorticotropic hormone [ACTH] stimulation test) and/or a gastrointestinal barium study. A barium study involves oral administration of a barium mixture – which is a thick, radiopaque liquid substance – which is followed by a series of radiographs (X-rays). Where barium is present, it does not permit the passage of the X-rays, making it appear white on the radiograph films. Accordingly, as the barium moves through the dog’s gastrointestinal tract, the veterinarian can visualize obstructions and other abnormalities that may exist in the esophagus, stomach, duodenum and small and large intestines.

Special Notes

Very young and very old dogs that lose their appetites, or are vomiting and having frequent diarrhea, can become dehydrated extremely rapidly. They should be seen by a veterinarian at the very earliest opportunity. An acute decrease in a dog’s body weight often indicates an acute loss of body water and is the most sensitive diagnostic tool for gauging dehydration. When a dog acutely loses approximately 12% or more of its body weight in water, the condition is considered to be life-threatening.

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