AbstractObjectivesTo document the incidence of hyperlactatemia in sick cats hospitalized for emergency care and to evaluate the prognostic utility of serial lactate measurements in cats with hyperlactatemia.DesignProspective observational study over a 10‐month period (July 2010–May 2011).SettingPrivate veterinary referral center with 24‐hour hospital care.AnimalsOne hundred and twenty‐three privately owned cats admitted to a private referral center.InterventionsBlood was collected by direct venipuncture from the jugular or medial saphenous vein at the time of hospital admission and at 6 and 24 hours following admission.Measurements and Main ResultsThe median plasma lactate concentration for all cats at admission (T0) was 1.89 mmol/L (17.0 mg/dL) (range: 0.3–12.48). Twenty‐three percent (28/123) of cats admitted were hyperlactatemic (ie, >2.87 mmol/L; >25.86 mg/dL) upon admission. Lactate concentration at presentation and serial lactate measurements were not found to be related with survival to discharge or correlated with duration of hospitalization. The overall survival rate of all cats in this study was 81%.ConclusionsThis study demonstrated that the incidence of hyperlactatemia in sick cats being admitted for hospitalization in a private referral center was 23%, and that lactate concentration on admission and serial lactate measurements over time were not prognostic in this group of hospitalized cats. Future studies are needed to evaluate the prognostic utility of lactate and serial lactate measurements in specific disease states and in a larger population of critically ill cats.