Impact of physical activity of individuals and creatine kinase on 99th percentiles of troponin I assays

Abstract

Determination of cardiac troponin I (cTnI) is one central means for diagnosis of myocardial infarction. Assay performance of three troponin I assays was compared previously in a large reference population detecting sex-differences in the 99th percentile only for the Dimension Vista cTnI assay. The present study examined the underlying effects. Values for cTnI were reused. Creatine kinase (CK) activity was determined in 2358 samples from blood donors. Information on physical activity was evaluated from health questionnaires. Using quantile regression data were analysed to investigate the impact of sex, physical activity, and CK on the 99th percentile of the cTnI assay. We report significant sex-differences for the 99th percentile of cTnI. Physical activity was significantly associated with cTnI values. Strong association of CK activity with cTnI values was detected only in men. Adjustment for CK in quantile regression abolished sex-differences in the 99th percentile. Two other contemporary sensitive cTnI assays were not relevantly affected by physical activity or CK. Sex-differences in the 99th percentile for the Dimension Vista cTnI assay arise from a positive association between cTnI and physical activity and were abrogated when data were adjusted for CK activity. These findings should be taken into account when using this assay.

Keywords: 99th percentile; Creatine kinase; Troponin I.