If a patient with suspected Non-ST-Elevation Myocardial Infarction (NSTEMI) has an initial negative Troponin 1 (Trop 1) result, when should the Troponin 1 test be repeated?

Troponin Repeat Timing in Suspected NSTEMI

If high-sensitivity troponin (hs-cTn) is available, repeat troponin at 1 hour after the initial measurement; if using conventional troponin assays, repeat at 3 hours after the initial measurement. 1, 2

Algorithm Based on Assay Type

High-Sensitivity Troponin (hs-cTn) Protocol

The 2020 ESC Guidelines provide the gold standard approach using validated 0h/1h or 0h/2h algorithms with assay-specific cutoffs. 1

• Repeat hs-cTn at exactly 1 hour (±10 minutes) after the initial blood draw to maximize safety and allow application of the ESC 0h/1h algorithm 1
• If the 1-hour window is missed, obtain the sample at 2 hours and apply the ESC 0h/2h algorithm instead 1
• Document the exact time of blood draw (±10 minutes) to ensure proper algorithm application 1

The 0h/1h algorithm stratifies patients into three categories: 1

• Rule-out: Very low baseline hs-cTn AND minimal delta change (assay-specific cutoffs in Table 5 of ESC guidelines)
• Rule-in: High baseline hs-cTn OR significant delta increase (assay-specific cutoffs)
• Observe: Patients not meeting rule-out or rule-in criteria require a third measurement at 3 hours 1

Conventional Troponin Protocol

If hs-cTn is unavailable, repeat conventional troponin at 3-6 hours after symptom onset (or time of presentation if symptom onset is unclear). 2, 3

• The American College of Cardiology recommends the 3-6 hour window to capture the characteristic rise and/or fall pattern essential for NSTEMI diagnosis 2
• Use time of ED arrival as the reference point if symptom onset time is ambiguous 2, 3

Extended Monitoring Beyond Initial Serial Testing

Obtain additional troponin measurements beyond the initial protocol if: 2, 3

• Clinical suspicion remains high despite initially normal values 2
• ECG changes are present (ST-segment depression, T-wave inversion) 3
• High-risk features exist: age ≥65 years, ≥3 CAD risk factors, prior coronary stenosis ≥50%, ≥2 anginal events in prior 24 hours 3
• Recurrent or ongoing chest pain develops 1

Late increases in cardiac troponin occur in approximately 1% of patients, so serial testing should continue if clinical suspicion persists. 1

Critical Caveats

Always integrate troponin results with detailed clinical assessment and 12-lead ECG—algorithms should never be used in isolation. 1

• A rising and/or falling pattern is essential to distinguish acute MI from chronic troponin elevation (e.g., renal failure, heart failure) 2, 4
• Do not fail to repeat troponin in high-risk patients despite initially negative results, as patients presenting very early may not yet have detectable elevations 2
• Do not rely solely on troponin values without considering clinical context and ECG findings 2

Practical Implementation

For hs-cTn assays, nursing teams should obtain blood samples at 0h and 1h irrespective of other clinical details to maximize safety and feasibility. 1

• If using conventional troponin and the patient presented ≥3 hours after symptom onset with normal ECG, a single negative troponin may be reasonable to exclude MI, though this is less safe than serial measurements 3
• Consider observation in a chest pain unit with serial ECGs and troponin at 3-6 hour intervals for patients with symptoms consistent with ACS but without objective evidence of ischemia 3

Prognostic Considerations

Even mildly elevated troponin levels carry significant prognostic value for both short-term and long-term mortality. 1, 3

• It may be reasonable to remeasure troponin once on day 3 or 4 in confirmed MI patients as an index of infarct size, though this is not required for diagnosis 2, 3
• hs-cTn T has greater prognostic accuracy than hs-cTn I, though both have comparable diagnostic accuracy 1