Cardiac troponin I in racing standardbreds.

Background: Upper reference limits for cTnI have not been established for healthy Standardbred racehorses.

Objectives: To establish cTnI upper reference limits for Standardbred racehorses and determine if increases in plasma cTnI concentration can be detected in 1-2 hours after a race.

Animals: Samples were obtained from 586 apparently healthy Standardbreds aged 2-14 years before racing and from the winners of 144 races 1-2 hours after the end of the race.

Methods: Prospective, observational study; convenience sampling; assay validation; and reference limits determinations were performed according to ASCVP guidelines. Plasma cardiac troponin I concentrations before racing were determined, potential outliers identified, and the 95th and 99th percentile upper reference limits calculated using nonparametric methods. The correlation between cTnI concentration and age, differences in median cTnI concentrations by subgroups and differences between cTnI concentrations before and after racing in winning horses were determined.

Results: The 95th and 99 th percentile upper reference limits for all horses excluding outliers were < 0.04 ng/mL and 0.06 ng/mL. There were no significant differences in cTnI concentrations based on age (P = .06), sex (P = .35), gait (P = .55), or race classification (P = .65) and a weak correlation of cTnI with age (ρ = 0.09, P = .03). There were no significant differences between cTnI concentrations before and after racing in winning horses (P = .70).

Conclusions And Clinical Importance: Because of lack of standardization across cTnI assays, the reference limits apply only to the Stratus CS immunoassay. Future studies looking at the effects of high intensity, short duration exercise on cTnI should consider sampling more than 2 hours after racing or using an ultrasensitive assay.