Can a point-of-care (POCT) high-sensitivity troponin T (hs-TnT) analyzer be used for rule-out of myocardial infarction (MI) and what are the criteria for its use?

From the Guidelines

Point-of-care high-sensitivity troponin T (hs-TnT) analyzers can be used for rule-out of myocardial infarction (MI) in emergency settings, but with careful consideration of their limitations and the clinical context, as indicated by the most recent guidelines 1. The primary criteria for using these devices include a single hs-TnT measurement below the 99th percentile upper reference limit, which in this case is 14 ng/dL, in patients presenting more than 3 hours after symptom onset. However, the use of POCT hs-TnT for rule-out of MI is generally recommended with a validated 0/1-hour or 0/2-hour algorithm, which may not be directly applicable with a POCT analyzer that only provides a qualitative result below the 99th percentile. For optimal implementation, patients should be risk-stratified using tools like the HEART score, with low-risk patients being most suitable for rapid rule-out protocols. The analyzer should be properly calibrated and maintained according to manufacturer specifications, with regular quality control checks. Healthcare providers must be trained in interpreting results within clinical context, as false negatives can occur in very early presenters (less than 2 hours from symptom onset). Some key considerations include:

• The 99th percentile upper reference limit should be derived from a sample size of at least 400 male and 400 female healthy individuals, as recommended by the IFCC and American Association of Clinical Chemistry guidelines 1.
• The use of sex-specific 99th percentile upper reference limits may be valuable, but this is not directly applicable to the POCT analyzer in question.
• Changing concentrations (deltas) can facilitate diagnosis and risk stratification of patients with suspected acute coronary syndrome, but this requires quantitative results, which may not be available with the POCT analyzer.
• The integration of hs-cTn with clinical decision pathways is crucial for accurate diagnosis and management of patients with suspected MI. In cases where the POCT hs-TnT result is below the 99th percentile, and the patient presents more than 3 hours after symptom onset, and is low-risk according to the HEART score, the POCT analyzer can be used for rule-out of MI. However, in cases where the result is above the 99th percentile, or the patient presents early after symptom onset, or is high-risk according to the HEART score, further evaluation with a quantitative hs-TnT assay and clinical correlation is necessary. It is also important to note that conditions such as type 2 myocardial infarction may become more common with the use of hs-cTn, and unstable angina may become less frequent but still occur, as indicated by the 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guidelines 1.

From the Research

Rule-Out Criteria for Myocardial Infarction (MI) Using POCT hs-TnT

The use of point-of-care (POCT) high-sensitivity troponin T (hs-TnT) analyzers for the rule-out of myocardial infarction (MI) has been explored in several studies.

• The study by 2 found that hsTnT concentrations < 6 ng/L at the time of ED arrival can rule out AMI with very high sensitivity and negative predictive value.
• Another study by 3 investigated the use of high-sensitivity troponin T for early rule-out of MI in recent onset chest pain and found that hsTnT taken at 0 and 2 h after presentation, together with ECG results, could identify patients suitable for early stress testing with a false negative rate for AMI of 1.2%.
• The study by 4 confirmed the ability of very low concentrations of high-sensitivity cardiac troponin (hs-cTn) on presentation to exclude acute myocardial infarction with high clinical sensitivity and negative predictive value.

Steps for Using POCT hs-TnT for Rule-Out of MI

To use POCT hs-TnT for rule-out of MI, the following steps can be taken:

• Measure hs-TnT levels at the time of ED arrival
• Use a cutoff value of < 6 ng/L to rule out AMI
• Consider using ECG results in conjunction with hs-TnT levels to improve diagnostic accuracy
• Be cautious when using POCT hs-TnT in older patients, women, and patients with underlying cardiac comorbidities

Limitations of POCT hs-TnT

• The study by 5 found that POCT troponin T is inferior to high-sensitivity troponin T for ruling out acute myocardial infarction in the emergency department.
• The study by 6 demonstrated reasonable sensitivity for detecting AMI using POCT hs-TnT, but highlighted the need for further evaluation of its diagnostic accuracy.

Cases Where POCT hs-TnT Can Be Used

POCT hs-TnT can be used in the following cases:

• Patients presenting to the ED with suspected cardiac chest pain
• Patients who are at least 2 hours from the onset of symptoms
• Patients who require rapid triage and transportation to appropriate care centers

Cases Where POCT hs-TnT Should Not Be Used

POCT hs-TnT should not be used in the following cases:

• Patients with ST-elevation AMI, cardiac arrest, or abnormal kidney function
• Patients who require more accurate diagnostic testing, such as laboratory-based hs-TnT assays
• Patients who have underlying cardiac comorbidities or are at high risk for AMI, as the sensitivity of POCT hs-TnT may be lower in these populations 2, 5