Biological variation of cardiac troponin in stable haemodialysis patients.

Abstract

Patients with end-stage renal failure exhibit a chronic elevation of serum cardiac troponin (cTn) concentration. In order to facilitate the diagnosis of myocardial infarction in these patients, it is necessary to distinguish an increased cTn concentration due to an acute event, from that being a manifestation of chronic elevation. The aim of this study was to gather biological variation data relating to two serum cTn assays, one, a hs-cTnT assay, the other a contemporary sensitive cTnI assay, among stable haemodialysis patients. It was hoped that this might inform as to the best way to use cTn assays to assist in the diagnosis of myocardial infarction in patients with end-stage renal failure. Eighteen stable haemodialysis patients were recruited, of whom 16 completed the study. Predialysis blood samples were collected weekly for 10 weeks during the second dialysis session of the week. Analytical CV (CVA), within-subject biological variation (CVI), between-subject biological variation (CVG), reference change value (RCV) and index of individuality (II) were determined for both assays. All samples had a serum hs-cTnT concentration above the 99th percentile for a healthy population compared to 29.4% for cTnI. For hs-cTnT, the long-term CVA was 2.1%, CVI 10.5%, CVG 64.2%, RCV 28.1% and log-normal RCV (rise/fall) 34.4%/-25.6%. The corresponding values for cTnI were 7.1, 20.2, 100.5 and 79.8%/-44.4%. The II was 0.17 and 0.2 for hs-cTnT and cTnI, respectively. Long-term biological variation of cTn in stable haemodialysis patients is similar to that in healthy individuals and in patients with stable coronary arterial disease. The low II for cTnI and hs-cTnT in stable haemodialysis patients indicates that population-based decision points are of limited value. Serial measurements are required to detect significant changes in cTn concentrations and support diagnosis of myocardial infarction in these patients.