Troponin is a protein found in the muscle cells of the body, with specific forms, troponin I and troponin T, being almost exclusive to the heart muscle. Under normal circumstances, these cardiac-specific troponins are present in the blood in extremely low, often undetectable, amounts. When the heart muscle sustains damage, its cells die and release their contents, including troponin, into the bloodstream.
A quantitative troponin test is a blood test designed to measure the precise amount of these cardiac-specific proteins in circulation. By quantifying the level of troponin, clinicians can gain insight into the presence and extent of heart cell damage.
The Role of the Troponin Test in Diagnosis
A troponin test is ordered in an emergency setting when an individual presents with symptoms suggestive of acute cardiac distress. A healthcare provider may order the test if a patient experiences symptoms such as:
- Chest pain or discomfort, which might be described as pressure, squeezing, or aching
- Pain that radiates to the jaw, neck, back, or one or both arms
- Shortness of breath
- Dizziness or lightheadedness
- Unexplained fatigue
The “quantitative” aspect of the test is important because it provides a specific numerical value for the troponin level, rather than a simple positive or negative result. The procedure itself involves a standard blood draw from a vein, usually in the arm, with no special preparation required from the patient.
Interpreting Quantitative Troponin Levels
Interpreting the results of a quantitative troponin test is a process that involves looking at both the absolute value and its change over time. In a healthy individual, cardiac troponin levels are so low that they cannot be detected by most standard tests. Different laboratories may have slightly different reference ranges, but a result below 0.04 nanograms per milliliter (ng/mL) is considered normal. An elevated level suggests that some form of heart muscle damage has occurred.
A single high reading is informative, but the pattern of change over several hours is often more diagnostically significant. For this reason, physicians frequently order serial troponin tests, drawing blood upon presentation and then again at specific intervals, such as three and six hours later. A clear rising and falling pattern in the troponin levels is a strong indicator of an acute myocardial infarction, or heart attack. This dynamic change reflects the initial release of troponin from damaged cells followed by its gradual clearance from the bloodstream.
Almost everyone who has had a heart attack will show elevated troponin levels within 12 hours of the event. The peak level of troponin can give an estimation of the extent of the damage to the heart muscle; a higher peak corresponds to more significant injury. Conversely, consistently normal troponin levels for 12 hours after chest pain begins make the diagnosis of a heart attack unlikely.
Causes of Elevated Troponin
The most frequent and significant reason for a markedly elevated troponin level is an acute myocardial infarction, commonly known as a heart attack. A heart attack occurs when blood flow to a part of the heart is blocked, depriving the muscle cells of oxygen and causing them to die. This cell death leads to a substantial release of troponin into the bloodstream.
However, other medical conditions can also cause troponin levels to increase, though often not with the same rapid rise-and-fall pattern seen in a heart attack. Chronic kidney disease is one such condition, as impaired kidney function can reduce the clearance of troponin from the blood. Other potential causes include inflammation of the heart muscle (myocarditis), severe infections (sepsis), a blockage in a lung artery (pulmonary embolism), an abnormally fast heart rate, or even intense physical exercise.
High-Sensitivity Troponin Assays
In recent years, the development of high-sensitivity troponin (hs-troponin) assays has refined the diagnostic process. These newer tests are capable of detecting much lower concentrations of troponin in the blood than previous generations of the test. The primary benefit of hs-troponin tests is the ability to more rapidly identify or exclude a heart attack.
Because they can detect very small changes, these assays can reveal a rise in troponin much sooner, sometimes within one to three hours of symptom onset. This allows physicians to make faster decisions regarding treatment. A consequence of this heightened sensitivity is that these tests may more frequently detect minor troponin elevations caused by conditions other than a heart attack.