What does a troponin level test?

Damaged heart tissue. Cardiac markers including ckmb and troponins measure damage to the heart muscle which occurs in a heart attack - the damaged/dying muscle will leak these into the serum which can be measured as blood tests. They start off "negative" - in the reference range - and then 4-6 hrs after the start of the heart attack they begin to rise - will eventually peak and over several days return to normal.