Rapid identification of falsely elevated serum cardiac troponin I values in a stat laboratory

To establish a rapid method for the stat laboratory to identify falsely elevated serum cardiac troponin I (cTnl) values caused by endogenous interferences.

Serum specimens with elevated cTnI were recentrifuged and cTnI was measured again. If the difference between first and second cTnI value was less than +/- 30%, the specimen was diluted 1:2, 1:5, and 1:10, and the cTnI was measured in the diluted specimens. If the cTnI concentrations did not change linearly with dilution, the specimen was referred to an outside lab for re-analysis of cTnI by a different immunochemical method.

Troponin I was elevated in 132 serum specimens. In 18 specimens, we attributed the elevation to the presence of fibrin or microparticles in the serum. Serial dilutions of 3 of the 114 remaining specimens produced nonlinear results. Overall, falsely elevated cTnI results were identified in 1.01% of all measurements.

Our method, which uses combined measurement of cTnI, creatinine kinase MB isoenzyme (CK-MB), and myoglobin, together with incubation, re-centrifugation, and serial dilution, is a practical method to identify falsely elevated serum cTnI values.