Biological variation of high sensitivity cardiac troponin-T in stable dialysis patients: implications for clinical practice.

BACKGROUND Changes in high sensitivity cardiac troponin-T (hs-cTnT) concentrations may reflect either acute myocardial injury or biological variation. Distinguishing between these entities is essential to accurate diagnosis, however, the biological variation of hs-cTnT in dialysis population is currently unknown. We sought to estimate the within- and between-person coefficients of variation of hs-cTnT in stable dialysis patients, and derive the critical difference between measurements needed to exclude biological variation with 99% confidence. METHODS Fifty-five prevalent haemo- and peritoneal-dialysis patients attending two metropolitan hospitals were assessed on 10 consecutive occasions; weekly for 5 weeks then monthly for 4 months. Assessments were conducted at the same dialysis cycle time-point and entailed hs-cTnT testing, clinical review, electrocardiography, and bioimpedance spectroscopy. Patients were excluded if they developed clinical or physiological instability. RESULTS In total 137 weekly and 114 monthly hs-cTnT measurements from 42 stable patients were analysed. Respective between- and within-person coefficients of variation were 83% and 7.9% for weekly measurements, and 79% and 12.6% for monthly measurements. Within-person variation was unaffected by dialysis modality or cardiac co-morbidity. The bidirectional 99% reference change value was -25% and +33% for weekly measurements, and -37% and +58% for monthly measurements. CONCLUSIONS The between-person variation of hs-cTnT in the dialysis population is markedly greater than within-person variation indicating that hs-cTnT testing is best applied in this population using a relative change strategy. An increase of 33% or a reduction of 25% in serial hs-cTnT concentrations measured at weekly intervals excludes change due to analytical and biological variation alone with 99% confidence.