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 t