In trying to ascertain the probable cause in an individual patient the first points to establish are :

• Does the animal have polyuria as well ? 
  • If so, this rules in the possibility of all of the above causes except ;:
    • Haemorrhage
    • Poisoning
    • Pyometra
    • Shock - eg endotoxic shock
  • If not - it rules in the possibility of 
    • Haemorrhage
    • oliguria 
      • acute renal failure
      •  terminal renal failure
    • Poisoning
    • Pyometra
    • Shock

     

• Is the animal able to concentrate urine if water is withheld ?
  • If so, this rules out the following possibilities :
    • Renal failure
    • Diabetes Insipidus
    • Fanconi syndrome
    • Primary renal glycosuria
  • If so, this does rules in the possibility of the following :
    • Diabetes mellitus
    • Cushings disease
    • Psychogenic polydipsia
    • Renal tubular acidosis

     

• Routine urinalysis
  • Presence or absence of glucose rules in diabetes mellitus, primary renal glycosuria, Fanconi Syndrome and renal glomerular damage

   

• Routine and specific  blood tests, examples
  • Blood glucose
    • if normal -  but glycosuria is present - rules in Fanconi Syndrome, glomerular disease and renal glycosuria, rules out diabetes mellitus.
    • If high and glycosuria is present - rules in Diabetes mellitus, and may be present in hyperadrenocorticism, and hepatic failure, but it  rules out Fanconi Syndrome, primary renal glycosuria, and other differential diagnoses.
  • kidney function
  • liver function
  • for Cushings disease
  • hypercalcaemia
  • acidaemia

   

• Radiography (or other imaging)
  • Pyometra
  • Phaeochromocytoma

It must be remembered that many of the causes of polydipsia occur in older age, so there is the possibility of concurrent diseases being present. for example diabetes and renal failure. This can make accurate diagnosis a problem.