cTnI Control (Cardiac Troponin I Control) is a crucial laboratory quality control material used to verify the accuracy and precision of diagnostic tests for cardiac troponin I, a protein released during heart damage (like a heart attack), ensuring tests (e.g., Bio-Rad, Abbott, Getein) give reliable results for detecting heart conditions. These controls come in different levels (low, normal, high) and are run alongside patient samples to monitor instrument performance and ensure clinical validity, especially for high-sensitivity troponin assays. 

In essence, if your cTnI control results are out of range, it signals a problem with the testing system, not necessarily the patient, prompting lab investigation before patient results are released.