What is the preferred biomarker, troponin T (troponin T) or troponin S (troponin S), for diagnosing cardiac injury in adults with a history of cardiovascular disease, hypertension, or other risk factors for cardiac injury?

Troponin T vs Troponin I for Diagnosing Cardiac Injury

Both cardiac troponin T and troponin I are equally preferred biomarkers for diagnosing myocardial injury, with no clinically significant difference in their diagnostic or prognostic performance. 1

Why Both Are Equivalent

Cardiac troponins (both T and I) are the preferred biomarkers for detecting myocardial necrosis based on their superior sensitivity and tissue-specificity compared to all other available markers. 1 The choice between troponin T or I should be based on local laboratory availability and assay validation rather than perceived superiority of one over the other. 1

Key Shared Characteristics

• Both troponin T and I are encoded by cardiac-specific genes and expressed exclusively in cardiac myocytes, providing nearly absolute myocardial tissue specificity. 1, 2

• Both markers demonstrate identical temporal release patterns: initial elevation within 3-4 hours from myocardial injury, with levels remaining elevated for up to 2 weeks due to proteolysis of the contractile apparatus. 2, 3

• Both provide equivalent diagnostic accuracy: within 6 hours of chest pain onset, 94% of MI patients had positive troponin T and 100% had positive troponin I in rapid assay studies. 2

• Both offer superior prognostic information compared to CK-MB, with risk proportional to the degree of elevation regardless of which troponin is measured. 1, 2

Practical Implementation

Measurement Protocol

Measure cardiac troponin (T or I) at presentation and repeat 3-6 hours after symptom onset to identify rising and/or falling patterns. 1 A single measurement is insufficient, as 10-15% of patients may not show troponin elevation initially. 2

For patients presenting within 6 hours of symptom onset, obtain additional troponin measurements beyond 6 hours if initial serial troponins are normal but electrocardiographic changes or intermediate/high-risk clinical features are present. 1

Diagnostic Threshold

An elevated troponin is defined as any value exceeding the 99th percentile of a healthy reference population, with optimal assay precision (coefficient of variation ≤10%) at this threshold. 1 The diagnosis of acute MI requires both:

• A rising and/or falling pattern of troponin values 1
• Clinical evidence that myocardial damage is due to ischemia (symptoms or ECG changes) 1

Historical Context on Specificity Concerns

Older literature documented false-positive troponin T results in skeletal myopathies and chronic renal failure, while troponin I showed interference from fibrin strands or heterophilic antibodies. 2 However, modern high-sensitivity assays have largely resolved these analytical issues, and both markers now demonstrate equivalent specificity. 1, 3

In patients with renal dysfunction, elevated troponin levels (whether T or I) originate from the myocardium rather than skeletal muscle, reflecting ongoing subclinical myocardial damage from volume overload, hypertension, or left ventricular hypertrophy. 2

High-Sensitivity Assays

High-sensitivity troponin assays (whether T or I) provide superior diagnostic accuracy compared to conventional assays by detecting myocardial injury in patients who would have undetectable levels with older assays. 1 These assays allow precise differentiation between normal and mildly elevated concentrations, detecting a relevant proportion of patients with acute MI who were previously missed. 1

Automated high-sensitivity assays in central laboratories are strongly preferred over point-of-care tests, as point-of-care devices demonstrate lower sensitivity, lower diagnostic accuracy, and lower negative predictive value. 1, 2

Critical Caveats

Do not use CK-MB, myoglobin, total CK, or other traditional cardiac enzymes when cardiac troponin is available, as these markers lack the sensitivity and specificity of troponin. 1

Always consider non-ACS causes of troponin elevation, including aortic dissection, pulmonary embolism, myocarditis, heart failure, tachyarrhythmias, and Takotsubo syndrome—all potentially life-threatening conditions that present with chest pain and elevated troponin. 2

For patients with diagnostic ECG abnormalities on presentation (new ST-segment elevation), do not delay diagnosis and treatment while awaiting biomarker results. 1