In a nonmyocardial cause of increased serum CK-MB, what is typically observed?

In a nonmyocardial cause of increased serum CK-MB, it is typically observed that there is an increase in CK-MB that is persistent. This is because nonmyocardial conditions, such as muscle injury or certain medical procedures, can lead to a sustained elevation of CK-MB levels. This persists over time as the CK-MB remains in circulation due to ongoing muscle damage or an inflammatory process.

In contrast, in myocardial injury, such as an acute myocardial infarction (AMI), the CK-MB levels rise rapidly and then subsequently decline as the damage is addressed. Therefore, the persistence of elevated CK-MB in nonmyocardial causes differentiates it from the transient spikes seen in myocardial infarctions.

The other choices provide different profiles that would not typically be seen in nonmyocardial cases. For instance, an increase in both the percent CK-MB and concentration (which is more indicative of cardiac injury) would not align with nonmyocardial causes. Similarly, the presence of increased troponin I (TnI) is more strongly associated with myocardial injury rather than non-cardiac causes. Lastly, while it might be observed that total CK can indeed show more modest increases in certain nonmyocardial conditions