Ultrasensitive quantification of cardiac troponin I by a Single Molecule Counting method: analytical validation and biological features

Abstract

Aim: To evaluate analytical and biological characteristics of the Singulex Clarity® cTnI assay, based upon Single Molecule Counting technology.

Methods: Assay's analytical sensitivity, precision, linearity, hook effect, cross-reactivity or interference by endogenous and exogenous substances, stability, 99th reference percentile [p99th] in EDTA plasma were evaluated in single or multi-site studies.

Results: Detection limit was 0.12 ng/L. Sensitivity was 0.14 ng/L at 20% CV (functional sensitivity) and 0.53 ng/L at 10% CV. Imprecision was 3.16%-10.0% in a multi-lot, single-site study, and 5.5%-12.0% in a single-lot, multi-site study; assay was linear from 0.08 to 25,000 ng/L. No hook effect was observed; any cross-reactivity/interference exceeded the 10%. Healthy subjects were recruited using clinical history, normal NT-proBNP and eGFR (n = 560) or plasma creatinine (n = 535) as inclusion criteria. cTnI was detectable in 96.8% of healthy subjects. The p99th were 8.01 (eGFR used) and 8.15 ng/L (plasma creatinine); both were measured with ≤5.7% CV. Median cTnI were significantly higher in older and male than in young and female subjects.

Conclusions: The Singulex Clarity cTnI assay show analytical features and % detection in healthy subjects that improve the corresponding values of most of the existing high-sensitivity cTnI assays.

Keywords: Analytical performance; Biological features; Cardiac troponin I; Single Molecule Counting.