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The Exam RoomBy The VeterinaryPracticeNow Desk3 min readOctober 2, 2026
Resting cortisol tracked APPLE scores but not mortality in 30 SIRS dogs
A prospective study of 30 SIRS dogs found cortisol tracked with APPLE scores but not with outcome, raising questions about its value in ICU triage.
Resting serum cortisol concentration was associated with illness severity but not with mortality in critically ill dogs with systemic inflammatory response syndrome, according to a prospective observational study published in the Journal of Veterinary Emergency and Critical Care. The finding matters because the study tested whether cortisol adds information about outcome in SIRS cases beyond what the APPLE score already provides, and in this sample, it didn't.
What the study found
Resting serum cortisol concentrations were higher in both the SIRS and non-SIRS groups compared with healthy controls (p < 0.001), but there was no significant difference between the SIRS and non-SIRS groups (p = 0.59). APPLE full scores were higher in the SIRS group compared with both the non-SIRS (p < 0.0001) and control (p < 0.0001) groups.
Resting serum cortisol concentrations were not associated with mortality (p = 0.33). APPLE full scores showed a statistically significant association with mortality (p = 0.03), which the authors describe as moderate evidence that the score can predict outcome.
How the study was built
The study enrolled client-owned dogs into three groups: 30 dogs with SIRS, 25 non-SIRS ICU cases, and 19 healthy controls at a university teaching hospital. Dogs with acute critical illness (less than 48 hours) admitted to the ICU were classified into SIRS and non-SIRS groups. Resting serum cortisol concentrations were measured before treatment. APPLE full and fast scores were calculated at admission, with outcome recorded for each dog.
This is a prospective observational study, which can show association but cannot prove causation. The design can tell whether cortisol tracks with severity scores or survival, but not whether cortisol itself influences outcome or whether treating based on cortisol would change anything. The SIRS sample of 30 dogs is small for drawing conclusions about cortisol's performance against APPLE scores in predicting mortality. The abstract does not state the study's power calculation, whether the SIRS sample was sized to detect a mortality difference, or what the actual mortality rate was in each group.
The number, and its error bars
For every 62.5 nmol/L (2.2 µg/dL) increase in resting serum cortisol concentration, APPLE full scores increased by 1 point (95% CI: 0.6 to 1.4). The true increase could be as low as 0.6 points or as high as 1.4 points per 62.5 nmol/L cortisol rise.
What the authors say it cannot tell you
The authors state that further studies enrolling larger numbers of cases may clarify cortisol's potential as a marker of outcome. The abstract does not specify what sample size would be needed or what effect size the study was powered to detect.
Who paid for it
The abstract does not state funding sources or conflicts of interest.
What this means for your practice
VeterinaryPracticeNow's read, not the study's. Everything in this section is our editorial interpretation for practice owners. The study does not claim any of it.
The study found cortisol tracked with how sick the dog looked on the APPLE score but did not add information about whether the dog survives. The APPLE score itself showed a statistically significant association with mortality, and cortisol did not. The calculation already done at admission outperformed the laboratory test in this sample.
For a practice running ICU cases, this is one data point on whether cortisol adds information when the APPLE score is already calculated. The severity score may tell more about survival than the cortisol draw in SIRS cases, though the small sample means the finding is preliminary. We'd watch for replication in a larger cohort. The authors call the APPLE mortality association moderate evidence, which suggests they're reading it cautiously given the sample size. We'd read it the same way.
