Clearance of cardiac troponin T with and without kidney function

Objective: The extent of kidney-dependent clearance of the cardiac damage biomarker cardiac troponin T (cTnT) is not known. Methods and results: We examined clearance of cTnT after injection of heart extracts in rats with or without clamped kidney vessels. The extent of degradation of cTnT to fragments able to pass the glomerular membrane and the kidney extraction index of cTnT was examined in human subjects. After a bolus injection of rat cardiac extract, simulating a large myocardial infarction, there was no significant difference in clearance of cTnT with or without kidney function. However, a slower clearance was observed late in the clearance process, when cTnT levels were low. When low levels of rat cardiac extract were infused at a constant rate to steady state, clamping of the renal vessels resulted in significant 2-fold reduction in clearance of cTnT. Over 60% of the measured cTnT in human subjects had a molecular weight below 17 kDa, expected to have a relatively free passage over the glomerular membrane. The extraction index of cTnT in three heart failure patients undergoing renal vein catheterization was 8-19%. Kidney function adjusted cTnT levels increased the area under the ROC curve for diagnosis of myocardial infarction of the cTnT analysis in an emergency room cohort. Conclusions: At high concentrations, often found after a large myocardial infarction, extrarenal clearance of cTnT dominates. At low levels of cTnT, often found in patients with stable cTnT elevations, renal clearance also contribute to the clearance of cTnT. This potentially explains why stable cTnT levels tend to be higher in patients with low kidney function. (C) 2017 Published by Elsevier Inc. on behalf of The Canadian Society of Clinical Chemists.