Which biomarker elevation is diagnostic of myocardial necrosis in NSTEMI but NOT present in unstable angina?

Explanation

## Biomarker Differentiation in NSTEMI vs Unstable Angina **Key Point:** The defining biochemical distinction between NSTEMI and unstable angina is the presence or absence of myocardial necrosis, detected by cardiac-specific troponins. ### Troponin as the Gold Standard Cardiac troponins (I and T) are: - Highly specific for myocardial injury - Detectable within 2–4 hours of symptom onset - Rise and fall over 7–14 days - The diagnostic marker that separates NSTEMI (troponin-positive) from unstable angina (troponin-negative) **High-Yield:** NSTEMI = ACS + elevated troponin + no ST elevation. Unstable angina = ACS + normal troponin + no ST elevation. ### Why Other Markers Are Not Diagnostic | Marker | NSTEMI | Unstable Angina | Specificity | |--------|--------|-----------------|-------------| | Troponin I/T | ↑ | Normal | Cardiac-specific | | CRP | Often ↑ | Often ↑ | Non-specific (inflammation) | | BNP | May ↑ | May ↑ | Non-specific (heart failure, renal disease) | | Myoglobin | ↑ | Normal | Muscle-specific, not cardiac-specific | **Clinical Pearl:** Myoglobin rises early (1–2 hours) but is found in skeletal and cardiac muscle, making it non-specific for myocardial necrosis alone. ### Diagnostic Algorithm ```mermaid flowchart TD A[Acute Coronary Syndrome]:::outcome --> B{ST elevation?}:::decision B -->|Yes| C[STEMI]:::outcome B -->|No| D[Check troponin]:::action D --> E{Troponin elevated?}:::decision E -->|Yes| F[NSTEMI]:::outcome E -->|No| G[Unstable Angina]:::outcome ```