title: Serum free cortisol fraction in healthy and septic neonatal foals.
abstract: BACKGROUND
  Relative cortisol insufficiency occurs in septic foals and impacts survival. Serum free (biologically available) cortisol concentration might be a better indicator of physiologic cortisol status than serum total cortisol concentration in foals.
  
  
  OBJECTIVE
  In septic foals, (1) low free cortisol concentration correlates with disease severity and survival and (2) predicts disease severity and outcome better than total cortisol concentration.
  
  
  METHODS
  Fifty-one septic foals; 11 healthy foals; 6 healthy horses.
  
  
  METHODS
  In this prospective clinical study, foals meeting criteria for sepsis at admission were enrolled. University-owned animals served as healthy controls. Basal and cosyntropin-stimulated total cortisol concentration and percent free cortisol (% free cortisol) were determined by chemiluminescent immunoassay and ultrafiltration/ligand-binding methods, respectively. Group data were compared by ANOVA, Mann-Whitney U-tests, and receiver operator characteristic curves. Significance was set at P < .05.
  
  
  RESULTS
  Basal % free cortisol was highest in healthy foals at birth (58 ± 8% mean ± SD), and was higher (P ≤ .004) in healthy foals of all ages (33 ± 6 to 58 ± 8%) than in adult horses (7 ± 3%). Cosyntropin-stimulated total and free cortisol concentrations were lower (P ≤ .03) in foals with shock (total = 6.2 ± 8.1 μg/dL; free = 3.5 ± 4.8 μg/dL versus total = 10.8 ± 6.0 μg/dL; free = 6.9 ± 3.3 μg/dL in foals without shock) and in nonsurvivors (total = 3.8 ± 6.9 μg/dL; free = 1.9 ± 3.9 μg/dL versus total = 9.1 ± 7.7 μg/dL; free = 5.5 ± 4.4 μg/dL in survivors). Free cortisol was no better than total cortisol at predicting disease severity or outcome in septic foals.
  
  
  CONCLUSIONS
  Serum free cortisol is impacted by age and illness in the horse. There is no advantage to measuring free over total cortisol in septic foals.
authors.affiliation: Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA, USA. khart4@uga.edu
authors.forename: K A
authors.initials: KA
authors.lastname: Hart
authors.forename: M H
authors.initials: MH
authors.lastname: Barton
authors.forename: D C
authors.initials: DC
authors.lastname: Ferguson
authors.forename: R
authors.initials: R
authors.lastname: Berghaus
authors.forename: N M
authors.initials: NM
authors.lastname: Slovis
authors.forename: G L
authors.initials: GL
authors.lastname: Heusner
authors.forename: D J
authors.initials: DJ
authors.lastname: Hurley
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000097:blood; D016022:Case-Control Studies; D005260:Female; D006734:Horse Diseases / Q000097:blood* / Q000401:mortality; D006736:Horses; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D018805:Sepsis / Q000097:blood / Q000401:mortality / Q000662:veterinary*; D012720:Severity of Illness Index
chemical_list: D006854:Hydrocortisone