Cardiac markers are blood tests that report what is happening to the heart muscle and to the heart as a pump. No single marker tells the whole story, so a skilled nurse reads them together with the patient's symptoms, the 12-lead ECG, the vital signs, and the overall clinical presentation. Some markers reflect myocardial injury (cells dying or being damaged), while others reflect cardiac stress and volume overload, ischemia, or impaired perfusion. The six markers you will meet most often are summarized below. | Marker | Normal (conventional) | What it measures | Key clinical use | |---|---|---|---| | Troponin I | < 0.04 ng/mL | Cardiac-specific contractile protein released with myocyte injury | Gold-standard test for myocardial infarction | | Troponin T | < 0.01 ng/mL | Cardiac-specific contractile protein released with myocyte injury | Confirming/monitoring myocardial injury | | CK (total) | ~30-200 U/L | Enzyme released by ANY muscle injury | Nonspecific muscle/cardiac injury, rhabdomyolysis | | CK-MB | < 5 ng/mL | CK isoenzyme enriched in cardiac muscle | Detecting re-infarction (fast return to baseline) |...