Comparing equations to correct total cortisol and total thyroxine hormone concentrations using haematocrit and total serum proteins in haemodiluted anaesthetised cats.

Use haematocrit-based correction equations to accurately interpret cortisol and thyroxine in haemodiluted anaesthetised cats.

This retrospective study investigated whether haemodilution affects total cortisol and total thyroxine concentrations in anaesthetised cats, and evaluated correction equations to unmask concentration changes obscured by dilution. Six cats underwent controlled haemorrhage followed by fluid replacement, with blood samples collected before haemorrhage and 30 minutes post-haemodilution. Total cortisol, total thyroxine, total serum protein (TSP), and haematocrit (HCT) were measured at both time points. Two correction equations were applied using either HCT or TSP as the correction variable. Results showed that haemodiluted cortisol concentrations were not significantly different from prehaemorrhage values, potentially masking a true physiological increase. Haemodiluted thyroxine concentrations were significantly lower than prehaemorrhage values, consistent with dilutional effects. When Equation A using HCT was applied, corrected cortisol concentrations revealed a masked increase consistent with the expected stress response to haemorrhage, while corrected thyroxine concentrations approximated prehaemorrhage levels. Correction using TSP was less reliable. These findings demonstrate that haemodilution can significantly alter measured hormone concentrations and that uncorrected values may misrepresent true hormonal status. Clinicians interpreting cortisol and thyroxine results in haemodiluted patients—such as those receiving aggressive fluid therapy or undergoing major haemorrhage—should apply haematocrit-based correction to avoid underestimating or failing to detect clinically relevant hormonal changes. This has particular relevance during anaesthesia and critical care scenarios in feline patients.

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