Preliminary investigation of circulating methaemoglobin fraction in cats with sepsis: a small exploratory study

ObjectivesThis exploratory study aimed to evaluate the methaemoglobin fraction in cats with sepsis, non-septic sick counterparts and healthy controls, and to assess the feasibility of using the methaemoglobin fraction as a biomarker for predicting clinically relevant outcomes such as duration of hospitalisation and mortality.MethodsMedical records were retrospectively searched for all cases of confirmed sepsis presenting to the intensive care unit (ICU) of two referral hospitals between September 2016 and January 2019 in institution A and between March 2019 and October 2024 in institution B, with a methaemoglobin measurement taken on admission. Records were also searched for cats presenting to the ICU of institution B between March 2019 and October 2024 that met 2/4 septic inflammatory response criteria without evidence of infection. The methaemoglobin levels of these cases and those of previously collected data from healthy cats (from both institutions) were compared with those of the septic population. Data from each institution were analysed separately.ResultsA total of 47 cats with sepsis were enrolled (23 in institution A and 24 in institution B), as well as 100 non-septic sick cats from institution B and 53 healthy controls (42 in institution A and 11 in institution B). Data from each institution were analysed separately. The median methaemoglobin fraction was significantly higher in control cats compared with septic cats in institution A (1.7%, 95% confidence interval [CI] 1.6-1.9 vs 1.1%, 95% CI 0.7-1.5; P = 0.03). There was no significant difference in median methaemoglobin levels between combined septic survivors vs non-survivors (0.5%, 95% CI 0.4-0.5 vs 0.9%, 95% CI 0.4-0.5; P = 0.5).Conclusions and relevanceThis exploratory study was unable to demonstrate a significantly increased circulating methaemoglobin fraction in cats with sepsis or an association between methaemoglobin fraction and survival outcome. These findings support the feasibility of further research and highlight the need for adequately powered standardised multicentre studies to clarify the biomarker's clinical utility.