A study evaluated medical records of 1916 dogs and 525 cats presented to an emergency hospital that had potassium levels checked within 24 hours of presentation. In the study,hypokalemia and hyperkalemia were considered with potassium concentration <3.5 mmol/L and >5 mmol/L respectively. 

Results:

Prevalence of abnormal potassium concentration was 27% in dogs and 40% in cats. 

Moderate to severe hypokalemia was seen in 3% of dogs and 8% of cats, and severe hyperkalemia were present in 2% of dogs and 7% of cats. 

Moderate to severe hypokalemia was most commonly associated with gastrointestinal disease (48% of dogs and 44% of cats) while moderate to severe hyperkalemia was most commonly associated with urinary tract disease (60% of dogs and 97% of cats). 

Dogs with hypokalemia and dogs and cats with hyperkalemia had significantly greater mortality than those with normokalemia. Dogs, but not cats,  with mild hypokalemia and mild hyperkalemia had higher mortality than dogs with normokalemia.

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Retrospective evaluation of the severity of and prognosis associated with potassium abnormalities in dogs and cats presenting to an emergency room (January 2014-August 2015): 2441 cases.