Effect of Health and Training on Ultrasensitive Cardiac Troponin in Marathon Runners.

PURPOSE: Cardiac troponin (cTn) is the gold standard biomarker for assessing cardiac damage. Previous studies have demonstrated increases in plasma cTn because of extreme exercise, including marathon running. We developed an easy-to-use, ultrasensitive assay for cardiac troponin I (cTnI) by combining single-molecule counting (SMC™) technology with dried blood spot (DBS) collection techniques and validated the assay on a cohort of marathon runners by correlating postmarathon cTnI elevations with training or risk variables. METHODS: An SMC-DBS method was developed for accurate and reproducible measurement of cTnI in fingerstick whole blood. Samples were collected from 42 runners both before and immediately after running a marathon. A similar collection was obtained from 22 non-running control individuals. Pre- and postrace questionnaires containing health and training variables were correlated with cTnI concentration. RESULTS: The assay quantified cTnI in all controls and marathon runners, both before and after the race. Prerace concentrations were significantly higher in marathon runners vs controls (median 3.1 vs 0.4 pg/mL; P < 0.0001). Immediate postmarathon concentrations were increased in 98% of runners (median elevation, 40.5 pg/mL; P < 0.001), including many above traditional cutoffs for acute myocardial infarction. Several health and training variables trended toward significant correlation with cTnI elevations. CONCLUSION: While further studies are needed to better understand the mechanisms and clinical implications of exercise-induced cTnI elevations, the present study suggests several variables that may be associated with such elevations and demonstrates a simple, cost-effective method for monitoring cTnI during exercise, managing chronic disease, and/or for assessing risk in large populations.

Expanding the Utility of High-Sensitivity Dried Blood Spot Immunoassay Testing with Single Molecule Counting.

BACKGROUND: Dried blood spot (DBS) testing has been used for years in newborn screening and for other applications when obtaining blood by venipuncture is impractical or expensive. However, several technical challenges have restricted the use of DBS testing to qualitative assays or to analytes that are present in relatively high concentrations. The application of high-sensitivity detection using single molecule counting (SMC™) technology can potentially overcome the limitations of DBS as specimen source. METHODS: A method was developed for reproducibly collecting, storing, and subsequently reconstituting DBS samples to be used with assays based on the SMC technology. Before extraction, DBS samples were scanned, and the blood spot area was calculated to normalize for sample volume and spot variability. DBS sample extraction was done using an efficient high-salt extraction buffer. DBS samples were tested using SMC-based cardiac troponin I (cTnI), prostate-specific antigen (PSA), and C-reactive protein (CRP) assays. RESULTS: The SMC-DBS assays showed reproducible sensitivity, precision, and the stability required for quantifying low-abundance biomarkers. These assays were not significantly impacted by normal variations in hematocrit or sample collection technique. Correlation coefficients obtained from method comparisons between SMC-DBS and laboratory-developed tests or Food and Drug Administration-cleared tests using traditional sample types were 1.08, 1.04, and 0.99 for cTnI, PSA, and high-sensitivity CRP, respectively. CONCLUSIONS: Combining DBS finger-stick blood collection with next-generation immunoassay technology will aid the expansion of DBS testing to protein biomarkers that are in low abundance or to low-volume samples, and will enable the development and adoption of DBS testing to far-reaching applications.