Troponin is a protein located in the muscle of the heart and helps control muscle contraction. There are actually three different parts that make up the entire protein: troponin C, troponin I, and troponin T. Troponin I and troponin T are also present in skeletal muscle, and troponin C is also present in smooth muscle. However, the lab test only measures troponin I and troponin T that are released from cardiac muscle. Usually, the lab will choose only one of the troponins (I or T) to measure since they both provide the same information.
As noted above, the main use for measuring troponin I and troponin T is to determine if the heart has been injured, usually from a MI. In the case of a heart attack, the troponins start to go up in the bloodstream in about 2-3 hours, and can stay increased for up to 10 days. The troponins are measured several times to trend their rise and fall to help determine if a MI has occurred.
Troponin can also be increased in many other conditions, and not just when part of the heart muscle dies. If the cardiac muscle loses its blood supply (ischemia), but does not suffer any tissue death, troponin can still be released into the bloodstream. Some other causes of an increased troponin include renal failure, congestive heart failure (CHF), arrhythmias, inflammation of the heart muscle or lining, severe systemic infection or inflammation (sepsis), pulmonary embolism (PE), pulmonary hypertension, rhabdomyolysis, hypertrophic cardiomyopathy, Prinzmetal's angina, intracranial hemorrhage, aortic dissection, Takotsubo cardiomyopathy (stress-induced), and intense exercise, to name a few. Pretty much anything that touches or involves the heart can cause troponins to be elevated, including surgical procedures.
In conclusion, troponin is an important test to order and is helpful for many conditions, not just for a heart attack. It is useful for determining prognosis and survival, so any instance of a rise in troponin should be fully investigated.
Sources:
Gibson, CM. Elevated cardiac troponin concentration in the absence of an acute coronary syndrome. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2011.
Jaffe, AS, and DA Morrow. Troponins and creatine kinase as biomarkers of cardiac injury. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2011.
Morgan, JP and TW Smith. Excitation-contraction coupling in myocardium. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2011.
If elevated troponin levels are indicative of so many diagnoses, as described in this great summary, wouldn't a troponin lab be less helpful for "many conditions"? MIs aside, it seems that it'd be more helpful to have other more specific labs for these diagnoses than a troponin lab, which is described here as common in many diagnoses. Just a thought.
ReplyDeleteRandy, great point. The first thing I think about when troponin is elevated is a MI, which must be ruled out first. This is done in combination with the patient's symptoms, presentation, and EKG findings. After MI is ruled out but the troponin is still increased, it's important to determine the cause because some other insult on the heart may be occurring. Then you would go ahead and order more specific tests for the other diagnoses on the list. A lot of things can cause an elevated troponin, but the lab test is most commonly ordered when MI is suspected.
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