Do you always get a troponin for patients who sustain blunt chest trauma?
Hopefully your answer is no. Of note, it is also NOT indicated as a screening test for those in whom you suspect a blunt cardiac injury (BCI). It can be normal in the setting of arrhythmias and it can be falsely elevated in the setting of catecholamine release or reperfusion injury from hypovolemic shock.
The initial screening test should include an ECG and a FAST ultrasound exam. If you have abnormal ECG findings, then a troponin is warranted (in addition to hospital admission).
Below summarizes a suggested algorithm from the recent EM Clinics of North America publication series. Definitive statements are challenging because there is no gold standard to diagnose BCI.
PV Card: Blunt Cardiac Injury
Adapted from 
Go to the ALiEM (PV) Cards for more resources.
- Bernardin B, Troquet J. Initial management and resuscitation of severe chest trauma. Emerg Med Clin North Am. 2012;30(2):377-400, viii-ix. [PubMed]