Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1263 page)

   Troponin elevation above the 99th percentile due to pathobiologic mechanisms (below) other than myocardial necrosis also have an elevated risk profile for short- and long-term morbidity.

   Troponin testing on hospital presentation followed by serial sampling with timing of sampling based on the clinical circumstances. cTnI may remain increased for ≤9 days, and cTnT may remain increased for ≤14 days.

   The long duration of increased cTn provides a longer diagnostic window than CK-MB but may make it difficult to recognize reinfarction. Recurrent reinfarction is diagnosed if a 20% increase in troponin is observed with 3–6 hours after the initial assessment.

   cTn is as sensitive as CK-MB during the first 48 hours after an AMI (>85% concordance with CK-MB); sensitivity is 33% from 0 to 2 hours, 50% from 2 to 4 hours, 75% from 4 to 8 hours, and approaching 100% from 8 hours after onset of chest pain. It may take ≤12 hours for all patients to show an increase. Sensitivity remains high for 6 days. Specificity is close to 100%.

   Serial cTn values may be indicator of cardiac allograft rejection. In selecting heart donors, cTnT >1.6 ng/mL predicts early graft failure with S/S = 73%/94%; cTnT >0.1 ng/mL predicts early graft failure with S/S = 64%/>98%.

   Troponin measurements are also useful in the differential diagnosis of skeletal muscle injury. Normal cTn values exclude myocardial necrosis in patients with increased CK of skeletal muscle origin (e.g., arduous physical exercise).

   Useful for diagnosis of perioperative AMI when CK-MB may be increased by skeletal muscle injury.

   Troponin may also be increased in <50% of patients with acute pericarditis. A value <0.5 ng/mL indicates no myocardial damage. A value >2.0 ng/mL indicates some myocardial necrosis.

   Interpretation

Increased In

   Myocardial infarction

   Cardiac trauma, including ablation, pacing, cardioversion, cardiac surgery

   CHF (acute and chronic)