Chart — Cardiac
Cardiac Marker Timeline Chart
Troponin I/T, high-sensitivity troponin, CK-MB, myoglobin, BNP, and NT-proBNP — elevation onset, peak timing, duration, clinical use, serial draw timing, and NCLEX application.
Educational use only. Reference ranges and serial draw protocols vary by institution and assay. Always use your facility's established ACS protocol and reference values. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
ACS Markers — Comparison Table
| Marker | Onset | Peak | Duration | Primary Use |
|---|---|---|---|---|
| Troponin I | 3–6 hours post-MI | 24–36 hours | 7–10 days | Gold standard for diagnosing acute MI — most specific cardiac marker. |
| Troponin T | 3–6 hours post-MI | 24–48 hours | 10–14 days | Equivalent to Troponin I for MI diagnosis — used when Troponin I assay unavailable. |
| High-Sensitivity Troponin (hs-Tn) | 1–2 hours post-MI | 12–24 hours | 7–14 days | Detects MI earlier than conventional troponin. |
| CK-MB (Creatine Kinase-MB) | 3–6 hours post-MI | 18–24 hours | 2–3 days (36–72 hours) | Historically used for MI diagnosis (largely replaced by troponin). |
| Myoglobin | 1–3 hours post-MI | 6–9 hours | 24 hours (returns to normal quickly) | Earliest rising marker after MI — rises before troponin. |
Detailed Marker Reference
Troponin I
Normal: < 0.04 ng/mL (conventional assay; varies by laboratory)
Timeline
Onset: 3–6 hours post-MI
Peak: 24–36 hours
Duration: 7–10 days
Serial Draws
On presentation, 3–6 hours later, then 6–12 hours later (per ACS protocol)
Clinical Use
Gold standard for diagnosing acute MI — most specific cardiac marker. Also elevated in PE, myocarditis, sepsis, renal failure, cardiac contusion.
NCLEX Focus
Primary marker for ACS diagnosis. Any elevation above the 99th percentile URL is significant — even small rises with a rise/fall pattern confirm MI.
Troponin T
Normal: < 0.01 ng/mL (conventional); varies by assay
Timeline
Onset: 3–6 hours post-MI
Peak: 24–48 hours
Duration: 10–14 days
Serial Draws
Same protocol as Troponin I
Clinical Use
Equivalent to Troponin I for MI diagnosis — used when Troponin I assay unavailable. Remains elevated longer than Troponin I, which aids detection of late presenters.
NCLEX Focus
Similar sensitivity and specificity as Troponin I. The longer elevation duration can help diagnose MI in patients presenting 3–7 days after symptom onset.
High-Sensitivity Troponin (hs-Tn)
Normal: Below the 99th percentile URL for the specific assay (sex-specific in some assays)
Timeline
Onset: 1–2 hours post-MI
Peak: 12–24 hours
Duration: 7–14 days
Serial Draws
0 and 1 hour (rapid protocol), or 0 and 2 hours; some facilities still use 0 and 3 hours
Clinical Use
Detects MI earlier than conventional troponin. Enables 0/1-hour or 0/2-hour rapid rule-in/rule-out protocols in ED settings.
NCLEX Focus
Increasingly the standard of care — allows faster discharge of low-risk chest pain. A negative hs-Tn at 0 and 2 hours with low clinical probability effectively rules out MI.
CK-MB (Creatine Kinase-MB)
Normal: < 5–10 ng/mL; CK-MB index < 2.5–3% of total CK
Timeline
Onset: 3–6 hours post-MI
Peak: 18–24 hours
Duration: 2–3 days (36–72 hours)
Serial Draws
Every 6–8 hours for 24 hours
Clinical Use
Historically used for MI diagnosis (largely replaced by troponin). Still useful for: (1) detecting reinfarction after initial MI (returns to normal faster); (2) distinguishing cardiac from skeletal muscle injury when total CK is elevated
NCLEX Focus
CK-MB returns to normal in 36–72 hours — if patient presents 5 days after symptoms, troponin will still be positive but CK-MB will have normalized. Re-elevation of CK-MB after normalization = reinfarction.
Myoglobin
Normal: < 90 ng/mL
Timeline
Onset: 1–3 hours post-MI
Peak: 6–9 hours
Duration: 24 hours (returns to normal quickly)
Serial Draws
Not routinely ordered for ACS diagnosis at most facilities
Clinical Use
Earliest rising marker after MI — rises before troponin. Very sensitive but NOT specific (also rises with any skeletal muscle injury, IM injections, rhabdomyolysis, strenuous exercise, renal failure). Rarely used as primary diagnostic today.
NCLEX Focus
High sensitivity (good for ruling OUT early MI with negative result) but poor specificity. If myoglobin is elevated AND troponin is rising = confirms MI. Isolated myoglobin elevation = consider rhabdomyolysis, muscle trauma.
BNP (B-type Natriuretic Peptide)
Normal: < 100 pg/mL (normal); 100–400 pg/mL (indeterminate); > 400 pg/mL (heart failure likely)
Timeline
Onset: Correlates with wall stress — hours after decompensation
Peak: Varies; reflects degree of fluid overload and ventricular stretch
Duration: Decreases with effective heart failure treatment
Serial Draws
On presentation for dyspnea; serial monitoring during HF treatment
Clinical Use
Marker of ventricular wall stress and fluid overload. Differentiates cardiac from non-cardiac dyspnea. Used to guide heart failure therapy and predict outcomes. Not a marker of ischemia.
NCLEX Focus
BNP is elevated in HEART FAILURE, not acute MI (unless ACS causes acute HF). BNP > 400 pg/mL = likely acute decompensated HF. BNP < 100 = dyspnea more likely non-cardiac.
NT-proBNP (N-terminal pro-BNP)
Normal: Age-dependent; generally > 125 pg/mL suggests HF (higher cutoffs in older patients)
Timeline
Onset: Same pathophysiology as BNP but longer half-life
Peak: Reflects volume overload and cardiac stress
Duration: Longer persistence than BNP (half-life 60–120 min vs 20 min for BNP)
Serial Draws
Similar to BNP
Clinical Use
Same clinical use as BNP — markers of ventricular stress. NT-proBNP is not affected by nesiritide (recombinant BNP), making it preferred monitoring marker in patients receiving BNP infusions.
NCLEX Focus
NT-proBNP values are approximately 5–10× higher than BNP for the same degree of heart failure. Do not confuse the two reference ranges on NCLEX scenarios.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with ACC/AHA ACS Guidelines; ESC hs-Troponin Protocols; HF biomarker consensus. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →