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TROPONINS

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REFERENCE RANGE
Trop I: <2.0 ug/L
Trop T: <0.1 ug/L
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INDICATIONS
Suspicion of myocardial damage.
Trop I and T are almost identical in their clinical usage.
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CHEMISTRY
A globular protein of muscle - is a central regulatory protein in muscle contraction. Troponin T binds to tropomyosin; Troponin I inhibits actin-myosin interactions.
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INTERPRETATION
Troponins are more sensitive and specific than CK or CK-MB. Usually ~none in the blood, so any elevation is a good indicator of myocyte damage.
Rise 4-12 hours after onset of symptoms (about the same time as CK, or slightly earlier). 50% positive within 4-5 hours, 99% by 12 hours. Ideal to do first collect at around 6 hours.
If specimen obtained less than 12 hours after onset of symptoms, collect a follow up at 6-12 hours later.
It is important to realise that angina without myocardial necrosis will not elevate troponins. Unstable angina, with minimal myocardial damage can cause elevations, though these definitions are being changed.
Remain elevated for 7 (TnI) to 10 days (TnT). 50% become negative at 7 days.
Also useful prognostically: higher 30 day mortality if troponin positive.
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TIPS AND PROBLEMS
[Renal Failure]: NB - may be elevated by renal failure - TnT especially, TnI to a lesser extent. This now thought due to ongoing small vessel damage to the heart related to the failure, rather than decreased clearance.

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