Abstract
Recent publications 1–3 have assessed serial changes in cardiac troponin (cTn) concentration in patients on haemodialysis. As discussed by Collinson and Gaze, 4 elevations of cTn in patients with renal failure portend a poor prognosis. However, an important question remains: what constitutes an elevation and how can change be used to further refine which patients are at risk? These three publications begin to address this issue. Jacobs et al. 1 measured cTnT and a precommercial high-sensitivity cTnT in predialysis specimens in 32 patients every two months over a six-month period. Roberts et al. 2 measured cTnT five times over 12 months in 81 patients: blood was taken before the middle dialysis session of the week. Hill et al. 3 measured cTnT on post-weekend, predialysis specimens in 60 patients weekly over 15 weeks.
From these publications there appear to be three groups of haemodialysis patients: cTnT concentration never increased, cTnT occasionally elevated and cTnT concentration increased on most occasions (with the cut-off being the 10% coefficient of variation [CV] concentration in all three studies). Importantly, patients with persistently increased cTn concentrations tended to be those patients with known cardiovascular disease 1 and those who were also at higher probability for a cardiovascular event and death as compared with those with no increased concentrations. 2 The group in which occasional increased concentrations were observed is the group in which change criteria may prove to be useful. Unfortunately, Roberts et al. 2 did not use this as a variable in their analysis, only the number of instances the cTnT cut-off was exceeded was used to classify the groups. The other two studies did not have outcome data but did report either an absolute range of concentrations measured in each patient (median [interquartile range, IQR] = 0.03 μg/L [0.02–0.06]) 1 or a change >0.06 μg/L from baseline to be considered as significant (taking into account intra-individual variability). 3
Importantly, change here is appropriately described in absolute terms given the current state of clinical assays and that the majority of patients had low (<0.10 μg/L) cTnT concentrations. At higher concentrations, a percentage change may be more appropriate. Data presented from an acute chest pain emergency department population, which used such change classification, consistent with the 2007 myocardial infarction definition (i.e. >3SD for lower concentrations and 20% for concentrations >0.10 μg/L) 5 demonstrated that change criteria were useful for risk stratification. 6 Evidence is accumulating to enable chronic worsening myocardial injury in haemodialysis patients to be recognized. However, with the advent of newer high-sensitivity cTn assays, 1,5 the majority of individuals will now have measurable cTn concentrations and thus change criteria will need to be revisited with respect to both the reference change value and the health outcomes.
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