For a patient with suspected non‑ST‑segment elevation myocardial infarction, should I use a high‑sensitivity troponin assay or CK‑MB as the cardiac biomarker?

Use High-Sensitivity Troponin, Not CK-MB, as Your Primary Cardiac Biomarker for NSTEMI

Cardiac troponins are the markers of choice for diagnosing NSTEMI and should be used as your primary biomarker—they have superior sensitivity and specificity compared to CK-MB, detect even minor myocardial damage that CK-MB misses, and provide critical prognostic information that guides therapy. 1

Why Troponin is Superior to CK-MB

Diagnostic Performance:

• Troponins have unsurpassed sensitivity and specificity for myocardial necrosis, allowing recognition of very small amounts of myocardial damage that CK-MB cannot detect 1
• High-sensitivity troponin assays are recommended over less sensitive assays because they provide higher diagnostic accuracy at identical cost 1
• Troponins remain elevated for up to 2 weeks after MI onset, providing a longer diagnostic window than CK-MB (which normalizes after 36 hours) 1

Prognostic Value:

• Troponin elevation identifies not just cell necrosis but also active thrombogenic plaques, indicating both prognosis and guiding therapy selection 1
• Patients with isolated troponin elevation (without CK-MB elevation) have significantly increased 30-day mortality risk, whereas isolated CK-MB elevation carries no significant risk difference compared to negative markers 1
• The higher the troponin level, the greater the risk of death—this dose-response relationship makes troponins powerful risk stratification tools 1

CK-MB Limitations You Must Know

Specificity Problems:

• CK-MB loses specificity in skeletal muscle disease, injury, or surgery—common scenarios in hospitalized patients 1
• CK-MB has low sensitivity for minor myocardial damage that troponins readily detect 1

Timing Limitations:

• CK-MB has low sensitivity during very early MI (less than 6 hours after symptom onset) 1
• CK-MB also has low sensitivity late after symptom onset (more than 36 hours) 1

When CK-MB Still Has Limited Utility

CK-MB remains useful only for:

• Detecting early reinfarction, due to its more rapid decline after MI compared to troponin 1
• Timing of myocardial injury when troponin is already elevated from a prior event 1

However, CK-MB should be considered a second-choice marker, not your primary diagnostic tool 1

Optimal Troponin Testing Strategy

Use High-Sensitivity Assays with Rapid Algorithms:

• Implement the 0h/1h algorithm (blood draw at 0 and 1 hour) as your best option for rapid rule-in and rule-out 1
• Alternatively, use the 0h/2h algorithm as your second-best option 1
• The traditional 0h/3h algorithm is acceptable when faster protocols are not validated for your specific assay 1

Diagnostic Thresholds:

• Use the 99th percentile of a reference population as your diagnostic cutoff 1
• Demonstrate a rising and/or falling pattern with at least one value above the 99th percentile to confirm acute MI 1
• Elevations beyond 5-fold the upper reference limit have >90% positive predictive value for acute type 1 MI 1

Critical Pitfalls to Avoid

Don't Misinterpret Troponin Elevations:

• Many cardiac pathologies beyond MI cause troponin elevation—including heart failure, myocarditis, Tako-Tsubo cardiomyopathy, tachyarrhythmias, and hypertensive emergencies 1, 2
• In renal dysfunction, do NOT attribute troponin elevation primarily to impaired clearance—cardiac conditions like chronic coronary disease or hypertensive heart disease are the real culprits 1, 2
• Aortic dissection and pulmonary embolism also elevate troponin and must be considered as differential diagnoses 1, 2

Timing Matters:

• Troponin has low sensitivity in the very early phase of MI (less than 6 hours after symptom onset), requiring repeat measurement at appropriate intervals 1
• Always integrate the time from symptom onset into your assessment of biomarker results 1

Context is Everything:

• Never rely solely on troponin without considering clinical presentation and ECG findings 1
• High-sensitivity assays detect troponin in 50-90% of healthy individuals, making serial measurements and delta changes crucial for diagnosis 1, 2

Point-of-Care Testing Caution

Avoid point-of-care troponin assays when possible:

• Most point-of-care assays cannot be considered sensitive or high-sensitivity assays 1
• Their shorter turnaround time is counterbalanced by lower sensitivity, lower diagnostic accuracy, and lower negative predictive value 1
• Central laboratory automated assays have been more thoroughly evaluated and are preferred 1

Bottom Line for Clinical Practice

Work with your laboratory to ensure:

• You're using contemporary high-sensitivity troponin assays 1
• You understand the specific diagnostic cutoffs for your hospital's assay 1
• Turnaround time for results does not exceed 1 hour 1

CK-MB is acceptable only as a second-choice marker when troponin is unavailable or for detecting early reinfarction 1. In all other circumstances, high-sensitivity troponin is your diagnostic standard for NSTEMI.