• Addison's disease;
  • effusion;
  • electrolytes;
  • endocrine diseases;
  • hypoadrenocorticism

Background: Sodium:potassium (Na:K) ratios are often reported in feline biochemical panels, although the importance of this measurement has not been investigated. Objectives: The aims of this study were to document the range of feline disease states associated with a decreased Na:K ratio, to determine the prevalence of this biochemical abnormality in a referral hospital population, and to identify any particular disease that was more likely to have a decreased Na:K ratio. Methods: A group of 49 cats with decreased Na:K ratios was compared with a group of 50 cats with normal Na:K ratios that were randomly selected from the same hospital population. Results: Twelve of the 49 cats (24.5%) had gastrointestinal disease, 10 (20.4%) had urinary disease, 8 (16.3%) had endocrine disease, 8 (16.3%) had cardiorespiratory disease, and 5 (10.0%) had diseases affecting other body systems. Six (12.2%) had artifactually decreased Na:K ratios. No cat was identified with hypoadrenocorticism. Statistical analysis revealed that, although none of these disease states was significantly over- or under-represented in the affected group, a significantly higher proportion of cats with decreased Na:K ratio had body cavity effusions (P= .025). Serum potassium concentrations were significantly higher in the affected group (P < .0001), but there was no significant difference in mean sodium concentration between the 2 groups. Conclusions: Decreased Na:K ratios frequently occur in cats with diseases other than hypoadrenocorticism, including cats with effusions. These findings should be considered when evaluating cats with this biochemical abnormality.