Why Troponin is 5 pg/mL and Not Zero in This Patient
High-sensitivity troponin assays detect troponin in 50-95% of healthy individuals, so a value of 5 pg/mL (5 ng/L) is within the normal detectable range and does not indicate cardiac injury. 1
Understanding High-Sensitivity Troponin Assays
The key distinction is between "detectable" and "elevated" troponin:
- High-sensitivity assays have a limit of detection between 1-5 ng/L, allowing measurement of troponin concentrations in most healthy people 1
- The diagnostic threshold for myocardial injury is the 99th percentile, which typically ranges between 10-20 ng/L depending on the specific assay used 1
- Your patient's value of 5 pg/mL (5 ng/L) is below the 99th percentile threshold, meaning it represents normal background troponin release, not pathologic cardiac damage 1
Why Healthy People Have Detectable Troponin
Normal physiologic turnover of cardiac myocytes releases small amounts of troponin into circulation:
- Cardiac troponins are structural proteins that undergo continuous low-level turnover even in healthy hearts 1
- High-sensitivity assays were specifically designed to detect these low concentrations that older conventional assays could not measure 1
- The ability to detect troponin in healthy individuals is actually a feature, not a flaw, as it allows better differentiation between normal and mildly elevated levels 1
Clinical Interpretation in This Case
Two key factors confirm no myocardial injury occurred:
- Both troponin measurements were identical at 5 pg/mL, showing no rising or falling pattern that would indicate acute cardiac damage 1, 2
- Serial measurements showing dynamic changes (rising and/or falling) are required to diagnose acute myocardial injury, not just a single elevated value 2, 3
- The normal sinus rhythm on ECG further supports the absence of acute coronary syndrome 1
Common Pitfall to Avoid
Do not interpret any detectable troponin as abnormal with high-sensitivity assays. The critical distinction is whether the value exceeds the 99th percentile upper reference limit (typically 10-20 ng/L), not whether it is detectable 1, 2. This patient's value of 5 ng/L represents normal background troponin present in healthy individuals, explaining why it is not zero.