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Updated: Jun 28, 2026
Cortisol Measurement in Koala (Phascolarctos cinereus) Fur
Published on: August 23, 2019
Comparing equations to correct total cortisol and total thyroxine hormone concentrations using haematocrit and total
Marinell Breytenbach1, Gareth E Zeiler1, Johan P Schoeman2
1Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria, Gauteng, South Africa; Section of Anaesthesiology & Critical Care Services, Valley Farm Animal Hospital, Pretoria, South Africa.
Objective:
To determine if haemodilution affects total cortisol and total thyroxine concentrations and, if so, to determine which equation and variables used in the correction factor would be useful to detect a change in concentration potentially masked by dilution.
Study Design:
Retrospective study on banked frozen samples.
Animals:
A group of six cats, 21 ± 1 months old (mean ± standard deviation) and 4.9 ± 1.2 kg.
Methods:
Total cortisol, total thyroxine, total serum protein (TSP) and haematocrit (HCT) were measured prehaemorrhage and 30 minutes after haemodilution [haemorrhage: 23.5 (19.6, 27.5) mL kg-1; Fluid: 22.5 (15.9, 29.1) mL kg-1]. Equations used to correct diluted hormone concentrations were: where MSHC is measured serum hormone concentration, X is either HCT (L L-1) or TSP (g L-1) used in the correction factor. Corrected hormone concentrations were compared to prehaemorrhage concentrations using a repeated measures ANOVA, agreement using repeated measures Bland-Altman, and correlation using concordance correlation coefficient. Significance was p < 0.05, and data reported as mean (95% confidence interval).
Results:
Prehaemorrhage cortisol was 69 (47, 92) nmol L-1 and not significantly different to the haemodiluted value of 63 (44, 82) nmol L-1 (p = 0.313). Prehaemorrhage thyroxine was 37 (31, 42) nmol L-1 and significantly higher than 19 (16, 22) nmol L-1 for the haemodiluted value (p < 0.001). Equation A using HCT identified a masked increase in cortisol [104 (78, 129) nmol L-1] and similar thyroxine [33 (27, 38) nmol L-1] concentrations.
Conclusion And Clinical Relevance:
Hormone concentrations are affected by haemodilution and require correction. Equation A using HCT corrected hormone concentrations that approximated expected changes in concentration in response to haemorrhage and haemodilution.
