Troponin: Troponin is a protein in the heart muscle. It is liberated into the bloodstream when heart muscles are damaged. Usually measured ones are troponin I and T (TnI and TnT). The estimation is a highly sensitive test to detect damage to the heart muscle. Levels in the blood increase significantly within 6 hours of the damage to heart muscle (usually a heart attack) and peaks at about 24 hours.
Is it possible to detect heart muscle damage using the test even before 6 hours?
Now several laboratories worldwide are offering high sensitivity estimations (hs troponin – hsTnI and hsTnT) testing. These tests can detect even minute quantities of the protein release. The trend is to take a sample as soon as the patient arrives in the emergency department and repeat another sample after one hour. The difference between the two values is known as delta troponin. A rise in value between two high sensitivity values is highly suggestive of fresh damage to the heart muscle and permits early diagnosis of a heart attack.
Can the levels be elevated without a heart attack?
Yes. Levels can be elevated if the heart muscle gets damaged due to other causes as well. For example direct injury to the heart muscle by trauma can cause rise in troponin level. Heart muscle injury can occur due to generalised sepsis. This also causes elevation of troponin levels. In kidney failure, troponin levels can be disproportionately elevated. This is more applicable to TnT rather than TnI. Still serial elevation of troponin levels can be taken as significant indicator of fresh heart muscle injury.
What is point-of-care troponin testing?
Point-of-care testing is testing at the very place where the patient is being taken care of like emergency department or intensive care unit. These testing devices gives rapid results, typically within 15 minutes. Early receipt of results right at the patient care spot allows rapid triaging of type of care to be given. There are of course some limitations compared to quantitative testing in the central laboratory. Some kits have an upper limit of measurement above which they just mention above the value and does not report the exact level.
Can a negative test always safely exclude a heart attack?
As it takes about 6 hours for the levels to rise significantly and about 24 hours to peak, very early testing can miss a heart attack. So the disease pattern (symptoms and physical examination findings) and other tests like ECG should be used to detect an early heart attack. When in doubt, always keep the person under observation and continue serial testing till a heart attack is confirmed or reliably excluded.