99th-Percentile Upper Reference Limit for the New Snibe High-Sensitivity Troponin I Assay in a Southeast Asian...

Background: The 99th-percentile upper reference limit (99% URL) is essential for high-sensitivity cardiac troponin I (hs-cTnI) assays to diagnose acute coronary syndromes. We derived the gender-specific 99% URLs for the new Snibe hs-cTnI assay and verified its high-sensitivity performance. Methods: The Snibe hs-cTnI assay has a claimed limit of blank/detection/quantitation of 0.5/1.0/2.0 ng/L, a precision of 5.67% (@ 9.83 ng/L), 4.65% (@ 21.0 ng/L) and 3.77% (@ 174 ng/L), an analytical measuring range of 1.00-500,000 ng/L, and a claimed 99% URL of 20.1/11.8/17.5 ng/L (males/females/overall). Assay precision was evaluated using kit control materials. A total of 846 (M 444, F 402) anonymized leftover samples from healthy individuals were assessed for the derivation of 99% URLs. Results: The inter-assay CV was 6.2/4.4% (@ 10.1/20.6 ng/L). The 10/20% CV corresponded to a concentration of 5.2/3.0 ng/L. The assay recorded detectable hs-cTnI values in 64% of women and 70% of men. Hs-cTnI values were significantly lower in females than males (females vs. males median 2.6 vs. 3.2 ng/L, Mann-Whitney p = 0.005). The derived 99% URL for the population was 7.7 ng/L (90% CI 6.93-22.8 ng/L) for women and 13.7 ng/L (90% CI 10.6-41.4 ng/L) for men. When confined to subjects ≥40 years old only, males had a 99% URL of 14.8 ng/L (n = 412, 90% CI 10.6-41.4 ng/L) and 8.1 ng/L (n = 377, 90% CI 6.95-22.8 ng/L) for females, respectively. Conclusions: The Snibe hs-cTnI assay fulfills the requirements of a hs-cTn assay. Gender-specific 99% URLs are derived for this assay and they increased with age.