Implementation of the 99th percentile as the upper reference limit for cardiac troponin (cTn) assays is a seemingly lucid recommendation, but, in reality, is incredibly complex. Lack of harmonization between cTn assays diminishes the ability to have a single medical decision point across manufacturer assay/instruments. Moreover, even within a single cTn assay there are several published values corresponding to the “99th percentile”. Variability in the determined value is primarily a function of population selection including: sample size, age, sex, exclusion criteria, and statistical methods. Given the complexities associated with this value, some countries have taken an expert consensus approach to endorsing harmonized, assay-specific, cTn 99th percentile values. The purpose of this manuscript is to highlight the intricacies associated with selecting a cTn 99th percentile and to review the approach that Australia used to endorse a nationwide upper reference limit for the Architect STAT hs-cTnI assay.