Circadian Variation of Cardiac Troponin

Acute myocardial infarction (AMI) is defined by an increase and/or decrease in the concentration of cardiac troponin, with at least one value above the 99th percentile value of the reference population together with evidence of ischemia. An objective tool to determine the magnitude of the cardiac troponin change is the use of reference change values (RCV). The basis for this tool is that, for a change to be significant, the difference in serial results must be greater than the inherent variation in two test results. The inherent variation of a laboratory test result is composed of analytical and within-subject biological variation. An important requirement to use RCVs is that the concentrations of cardiac troponins fluctuate randomly around a homeostatic set point in cardio-healthy individuals. Verification of this important condition has never been performed, and violation of this condition would preclude the use of RCV's in clinical practice.