Yes, the blood tests do vary at 15 mnutes and 7 hours. Best earliest BLOOD TEST indication of heart attack
is now the Troponin test
. This is used reliably by ER's. If the troponin is elevated the patient is admitted for further evaluation ASAP. Other cardiac enzymes can also detect cardiac damage. The time of the initial incident can be deduced by the timing of the elevation of the cardiac enzymes which rise at different rates. Another early predictor of cardiac problems is the High sensitivity CRP - and BNP as an early indicator of CHF. Other tests like EKG are also used to diagnose and treat heart patients.
The earliest the problem is detected the better because clot busting drugs may be able to limit the amount of damage if given early enough. These clot busting drugs will, however, alter the cardiac enzyme results.