## Troponin in NSTEMI vs Unstable Angina **Key Point:** The defining biochemical difference between NSTEMI and unstable angina is the presence of myocardial necrosis, detected by elevated cardiac biomarkers (troponin or CK-MB). ### Troponin Kinetics in NSTEMI 1. **Rise and Fall Pattern**: Troponin begins to rise within 2–4 hours of myocardial injury 2. **Peak**: Typically peaks at 24–48 hours 3. **Normalization**: Returns to baseline over 7–14 days 4. **Diagnostic Threshold**: At least one troponin value must exceed the 99th percentile upper reference limit (URL) ### Unstable Angina - **Troponin remains negative** throughout the clinical course - Represents reversible ischemia without myocardial necrosis - Diagnosis is clinical + ECG changes (ST depression, T-wave inversion) without biomarker elevation **High-Yield:** The rise-and-fall pattern (serial troponins) is more specific than a single elevated value and helps exclude chronic troponin elevation (chronic kidney disease, heart failure). **Clinical Pearl:** High-sensitivity troponin assays detect myocardial injury earlier (within 1–3 hours) and improve early rule-out protocols, but the rise-and-fall pattern remains the gold standard for acute myocardial infarction diagnosis. ### Table: Biomarker Comparison | Feature | Unstable Angina | NSTEMI | | --- | --- | --- | | **Troponin** | Negative | Elevated (rise and fall) | | **CK-MB** | Negative | May be elevated | | **Myocardial necrosis** | Absent | Present | | **ECG** | ST depression, T-wave changes | ST depression, T-wave changes | | **Prognosis** | Lower risk | Higher risk | [cite:Harrison 21e Ch 297]
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