What does elevated troponin level mean?
An elevated troponin is in general concerning for heart damage until proven otherwise. It can be from a heart attack due to a blockage or due to other conditions that place strain on the heart such as heart failure or critical illness. As discussed below there are other, non cardiac causes of a troponin elevation.
What level of troponin indicates heart attack?
The level of troponin that indicates a heart attack is the level above the reference range. For example if the normal reference range is listed as 0.00 – 0.40. Then 0.41 is technically positive although very weakly so, and 10 is very positive. Levels above the reference range may mean heart damage, but there are other causes also. When interpreting a troponin level it is important to know the reference range of the reporting labaratory.
What causes high levels of troponin?
Damage to the heart muscle cells are the classic cause of high troponin. There are many many other causes such as kidney disease, stroke, infection, pneumonia, critical illness and many others.
Often people are hospitalized and they go home with a copy of their blood tests, one of which is a troponin level. Recently, someone asked me whether they should be worried about a heart attack after they noticed an elevated troponin level on the blood tests listed on their discharge paperwork.
What is the normal troponin level?
A normal troponin level is that within the normal reported reference range. So if the lab says < 0.04 is normal, then 0.03 and 0.02 and 0.o01 etc. are all normal!
All About Troponin
Diagnosing a heart attack used to be relatively straight forward, or so we thought. A patient would come in with chest pain, have changes on the EKG heart tracing suggestive of a heart attack, and a number of blood tests were sent off looking at levels of markers which if positive implied heart damage. When heart muscle tissue is damaged it releases molecules in to the blood stream, levels of which are known as cardiac markers. We would put this information together and then determine that the likelihood of heart attack was high when these tests were positive. Appropriate further tests were then done.
The problem was that the blood tests (in the days before troponin levels) did not pick up every heart attack, as they were not sensitive enough. Patients who were determined to be having a heart attack would typically get tests such as a heart cath where dye is injected in to the arteries, to see if there were blockages that caused the attack. Tests like echocardiograms (ultrasounds of the heart) were done to see if there was any visible damage to the heart muscle tissue.
There is clearly a difference between heart attacks that involve a whole major artery and result in large areas of heart muscle damage versus those involving the small end of an artery with no clearly seen areas of heart muscle damage. The old blood tests (before troponin levels were discovered) in many cases did not pick up a lot of the smaller heart attacks, as they were not sensitive enough.
The Start Of A New Era – The Benefits of Using Troponin
Then in the 1990’s a blood test measuring troponin levels came in to use. Troponin is a substance is released in to the blood when heart muscle is damaged. It is incredibly more sensitive than the old markers used. It turns out that we were missing many heart attacks using just the older blood tests, (although probably not the large ones). Suddenly now that we had troponin levels, when people came with chest pain, we would send this test, and bingo:
Chest Pain + Positive Troponin Level = Heart Attack
A higher troponin level to a degree probably meant a bigger attack, but we were now sending more patients for further tests and picking up damage. In fact, just the presence of high troponin levels is a reason to immediately call a cardiologist, because the test was so sensitive it must mean heart damage right!
How to Read Your Levels
There was a problem however, although the troponin test was great in that it did not miss heart attacks, it was not specific for heart attacks alone. It was realized that many patients with critical illnesses, infections, head injuries, kidney disease …(the list goes on and on) could have an elevated troponin level which may have been linked to an indirect effect on the heart muscle (We call this a type II myocardial infarction). When these patients had heart tests however, not all of them had large obstructions or damage. This was certainly not due to complete blockage of a heart artery in the classical way we think of a heart attack. Importantly, not all these patients needed to be taken for further heart procedures. In the early days of troponin testing many of these patients did undergo further heart tests and procedures, while we figured out how to use the troponin test best.
Much research has been done in to what these elevations of troponin in the absence of obstructive heart disease mean. We know that it is not a good thing, and it may be a marker / red flag for other illnesses of problems. Importantly it needs to be interpreted in the clinical context. So now you see how a patient who is admitted to the hospital with lets say a head injury or trauma or significant infection… may have mild elevation of troponin. Depending on the clinical context, many of these patients may not need further invasive tests. Often these patients may have a stress test, and if that is normal, and the heart pumping function remains normal, we are reassured that the prognosis might be good.
Its important to note however that each case should be individualized and their risk determined appropriately ideally by a cardiologist, as of course a heart that has existing disease is of course likely to be more sensitive and result in release of troponin in result of stress to other conditions. The skill is to make sure those patients are investigated appropriately, where as those with a low risk don’t need to undergo potentially risky and invasive tests.