Troponin-I (TNI) is a cytological protein forming part of the contractile apparatus in cardiac muscle cells. Cardiac myocyte damage leads to release of TNI into the bloodstream. Elevated TNI levels are a highly specific indicator of active myocardial damage, being found in very low concentrations in other muscle types.
Causes of elevated TNIH include myocardial injury due to:
Primary cardiac disease
• myocardial infarction
• myocarditis
• pericarditis
• myocardial toxicity e.g. monensin intoxication
Non-cardiac diseases
• systemic inflammatory diseases
• chronic lung disease, pneumonia
• renal failure
• shock
• strangulating and inflammatory acute abdominal disease
To order the TNIH test please send your patient serum sample to Gribbles along with your submission form (available to download at gribblesvets.com.au/veterinarians/ordering-a-test)
FAQs
1. Does TNIH increase with skeletal muscle injury?
No. TNIH is highly specific for cardiac muscle. There is no interference from creatine kinase or other skeletal muscle cellular proteins.
3. What is the half-life of TNIH?
By conventional assay troponin half-life is less than one hour.
3. Can TNIH testing be added to a profile?
TNIH may be added if the sample is less than 24 hours old and has been refrigerated. TNIH results after this time may be unreliable and a new sample is required.
4. How does the assay differ from conventional TNI testing?
TNIH is highly sensitive at the lower end of the clinical range, allowing more accurate measurement and tracking of myocardial injury. High sensitivity troponin assays are estimated to be ten times more sensitive than conventional TNI assays, and allow quantification of troponin concentrations at the low levels found in healthy animals. Due to significant inter-assay variability, TNIH and conventional TNI results from different laboratories are not directly comparable.
5. Will TNIH increase after exercise?
Studies using conventional TNI assays rather than high sensitivity assays have found either no increase or mild increases in some horses only after training or racing 1-5. Few studies have used the new high sensitivity assays to assess troponin kinetics in healthy equine athletes. In one study, high intensity, short duration exercise increased TNIH to peak at 3 hrs, then returned to normal by 12 hrs, but TNIH values did not exceed the high end of the normal reference range 6.
6. What is the clinical significance of elevated TNIH?
While equine-specific studies are lacking, increasing TNI has been shown to have prognostic significance in both cardiac and non-cardiac disease in other species 7. Elevated troponin has been associated with non-survival in cases of acute abdominal disease and heart disease in horses 8. Marked troponin elevations in inflammatory disease indicate myocardial damage and may reflect higher severity of disease.
Sampling protocol
Sample required:
Serum (gold-top gel or red-top plain tube). Plasma is unsuitable as reference ranges are based on serum.
Minimum volume:
• 1 ml serum
Use the same tube type (gold or red top) when serial sampling an individual patient.
Allow the sample to clot before centrifugation and separating the serum.
Tubes must be tightly capped for transport.
Ship serum samples frozen if there may be a delay in transport (testing must be performed within 24 hours for refrigerated samples).
Species:
TNIH is currently available for horses.
References
1. Begg LM, Hoffmann KL, Begg AP. (2006) Serum and plasmacardiac troponin I concentrations in clinically normal Thoroughbreds in training in Australia. Aust Vet J 84:336–337.
2. J. Slack, R.C. Boston, L. Soma, and V.B. Reef (2012) Cardiac Troponin I in Racing Standardbreds. J Vet Intern Med 26:1202–1208.
3. Phillips W, Giguere S, Franklin RP, et al. (2003) Cardiac troponin I in pastured and race-training Thoroughbred horses. J Vet Intern Med 17:597–599.
4. Nostell K, Haggstrom J (2008). Resting concentrations of cardiac troponin I in fit horses and effect of racing. J Vet Cardiol 10:105–109.
5. Holbrook TC, Birks EK, Sleeper MM, et al. (2006) Endurance exercise is associated with increased plasma cardiac troponin I in horses. Equine Vet J Suppl 36:27–31.
6. E. Shields, I. Seiden-Long, S. Massie, and R. Leguillette (2018) 24-Hour Kinetics of Cardiac Troponin-T Using a “High-Sensitivity”Assay in Thoroughbred Chuckwagon Racing Geldings after Race and Associated Clinical Sampling Guidelines J Vet Intern Med 32:433–440.
7. T. M. Rossi, W. G. Pyle, M. G. Maxie, D. L. Pearl and P. W. Physick-Sheard (2014) Troponin assays in the assessment of the equine myocardium Equine Veterinary Journal 46:270–275.
8. Fennell, L. C. (2010). Use of cardiac troponin in the diagnosis of heart disease in horses. Masters Research thesis, Faculty of Veterinary Science, The University of Melbourne.