Ep 15 - Understanding Troponin - Part 2

Understanding High Sensitivity Troponins: A Guide for Emergency Physicians

Welcome to the St. Emlyn's podcast. I'm Ian Beardsell and I'm Rick Bodden. This is part two of our troponin special where we delve deeper into high sensitivity troponins (hs-Tn) and their significance in emergency medicine. Today, we'll explore the nuances of hs-Tn assays and how they can enhance our work in the emergency department (ED).

Introduction to High Sensitivity Troponins

High sensitivity troponins (hs-Tn) have transformed how we detect and manage myocardial infarctions (MI) in emergency settings. Unlike traditional assays, hs-Tn tests detect much lower concentrations of troponin, a protein released during myocardial injury, allowing for earlier and more accurate detection of cardiac events.

Analytical Sensitivity vs. Diagnostic Sensitivity

Understanding the difference between analytical and diagnostic sensitivity is crucial. Analytical sensitivity refers to the assay's ability to detect low concentrations of troponin, whereas diagnostic sensitivity relates to the test's performance in diagnosing acute myocardial infarctions (AMI).

Key Points on Analytical Sensitivity:

• Detection Threshold: High sensitivity troponin assays can detect troponin in over 50% of healthy individuals.
• Precision: These assays have a coefficient of variation (CV) of less than 10% at the diagnostic threshold, ensuring consistent results.

Diagnostic Sensitivity:

• Improved Detection: Studies show hs-Tn assays have a higher diagnostic sensitivity (90-92%) compared to older assays (80-85%).
• Early Rule-Outs: This makes hs-Tn particularly valuable for ruling out AMI in patients presenting with chest pain in the ED.

High Sensitivity Troponin Assays: A Closer Look

To illustrate, let's focus on the Roche troponin T high sensitivity assay:

• 99th Percentile Cutoff: 14 nanograms per liter.
• Detection Range: Can detect levels as low as 3 nanograms per liter.
• Higher Readings: It's common for hs-Tn assays to give higher readings than older assays for the same sample, which affects the diagnostic threshold.

The Balance Between Sensitivity and Specificity

While hs-Tn assays improve sensitivity, they may reduce specificity:

• More Positives: Lowering the diagnostic threshold results in more positive results, increasing diagnostic sensitivity but reducing specificity.
• Predictive Value: For example, a positive hs-Tn T result at patient arrival has a specificity around 70% and a positive predictive value of 50%.

Using High Sensitivity Troponins in the Emergency Department

Early Rule-Out Protocols: The most significant advantage of hs-Tn assays is their potential to expedite the rule-out process:

• Zero and Three-Hour Protocols: Studies suggest that hs-Tn assays can effectively rule out AMI with samples taken at 0 and 3 hours after arrival, instead of the traditional 6-hour wait.
• Efficiency: This protocol can significantly speed up patient throughput in the ED, reducing congestion and wait times.

Understanding Deltas: Delta refers to the change in troponin levels between tests:

• Absolute vs. Relative Deltas: Absolute changes (e.g., an increase of 10 nanograms per liter) are often more reliable than relative percentage changes.
• Clinical Context: It's crucial to interpret deltas in the context of the patient's overall clinical picture.

Practical Considerations for Emergency Physicians

Incidental Troponin Elevations: With increased testing at the front door, incidental findings are inevitable:

• Low Pre-Test Probability: In patients with a low pre-test probability of AMI (e.g., mechanical falls), a positive hs-Tn result often does not indicate AMI.
• Clinical Judgment: Consider repeating the test and evaluating the patient's history and clinical presentation before making a decision.

Patients with Comorbidities: Troponin levels can be elevated in patients with various comorbidities:

• Age and Chronic Conditions: Older patients and those with conditions like LV dysfunction may have higher baseline troponin levels.
• Reference Ranges: Use broader reference ranges for patients with comorbidities, as suggested by studies from Paul Collins and colleagues.

Future Directions and Guidelines

Ongoing Research: Research and guidelines on hs-Tn usage are continually evolving:

• NICE Guidelines: Recommendations on using hs-Tn in clinical practice are expected to be published, providing clearer protocols for emergency physicians.
• Early Adoption: As new evidence emerges, early adopters must balance innovation with patient safety.

Point-of-Care Testing: While hs-Tn assays currently require large analyzers, point-of-care testing remains a goal:

• Future Developments: Advances in technology may eventually make hs-Tn testing available at the bedside, further streamlining ED workflows.

Conclusion

High sensitivity troponins represent a significant advancement in the early detection and management of myocardial infarctions in the emergency department. By understanding the nuances of analytical and diagnostic sensitivity, utilizing early rule-out protocols, and interpreting results within the clinical context, emergency physicians can leverage these assays to improve patient care. As always, ongoing research and adherence to evolving guidelines will be essential in optimizing the use of hs-Tn in clinical practice.

We hope this podcast helps you better understand the complexities and advantages of high sensitivity troponins. For more insights and updates, stay tuned to the St. Emlyn's blog and feel free to reach out with your questions and experiences. Together, we can continue to advance emergency medicine for the benefit of our patients.