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Sex-Specific 99th Percentile Upper Reference Limits for High Sensitivity Cardiac Troponin Assays Derived Using a Universal Sample Bank

BACKGROUND

How to select healthy reference subjects in deriving 99th percentiles for cardiac troponin assays still needs to be clarified. To assist with global implementation of high sensitivity (hs)-cardiac troponin (cTn) I and hs-cTnT assays in clinical practice, we determined overall and sex-specific 99th percentiles in 9 hs-cTnI and 3 hs-cTnT assays using a universal sample bank (USB).

METHODS

The Universal Sample Bank (USB) comprised healthy subjects, 426 men and 417 women, screened using a health questionnaire. Hemoglobin A1c (>URL 6.5%), NT-proBNP (>URL 125 ng/L) and eGFR (<60 mL/min), were used as surrogate biomarker exclusion criteria along with statin use. 99th percentiles were determined by nonparametric, Harrell--Davis bootstrap, and robust methods.

RESULTS

Subjects were ages 19 to 91 years, Caucasian 58%, African American 27%, Pacific Islander/Asian 11%, other 4%, Hispanic 8%, and non-Hispanic 92%. The overall and sex-specific 99th percentiles for all assays, before and after exclusions (n = 694), were influenced by the statistical method used, with substantial differences noted between and within both hs-cTnI and hs-cTnT assays. Men had higher 99th percentiles (ng/L) than women. The Roche cTnT and Beckman and Abbott cTnI assays (after exclusions) did not measure cTn values at ≥ the limit of detection in ≥50% women.

CONCLUSIONS

Our findings have important clinical implications in that sex-specific 99th percentiles varied according to the statistical method and hs-cTn assay used, not all assays provided a high enough percentage of measurable concentrations in women to qualify as a hs-assay, and the surrogate exclusion criteria used to define normality tended to lower the 99th percentiles.

5th generation cardiac troponin I and T assays in clinical routine - A head-to-head comparison with data from the Linz troponin (LITROP) study

BACKGROUND

In Europe, clinicians use so called high-sensitivity assays for the measurement of cardiac troponin I and T (i.e., hs-cTnI and hs-cTnT assays, also termed 5th generation assays) since several years. We aimed at performing a head-to-head comparison of two 5th generation assays in "real life use".

METHODS

We studied 3588 consecutive patients presenting to an emergency department. We used both, a hs-cTnI assay from Abbott and a hs-cTnT assay from Roche in clinical routine. We assessed (1) the capabilities of hs-cTnI and hs-cTnT for the prediction of 3.7 year all-cause mortality; (2) discordant diagnoses of myocardial injury by hs-cTnI and hs-cTnT according to the European gender-neutral 99th percentile upper reference limits (i.e., 26 ng/L and 14 ng/L, respectively); and (3) analyte kinetics in patient with serial troponin measurements.

RESULTS

With respect to prognosis of all-cause mortality, the AUC of hs-cTnI was 0.81 (95% CI, 0.80-0.82), and the AUC of hs-cTnT was 0.85 (95% CI, 0.84-0.86). With respect to discordant diagnoses, 21% of the 3588 patients were classified as having myocardial injury by hs-cTnT but not by hs-cTnI, and < 1% were classified as having myocardial injury by hs-cTnI but not by hs-cTnT. In the patients with serial blood sampling, the median delta values were 6.3 ng/L and 25% for hs-cTnI, and 4.2 ng/L and 16% for hs-cTnT.

CONCLUSION

We found different characteristics of the Abbott hs-cTnI and the Roche hs-cTnT assays, especially when using the European gender-neutral 99th percentile upper reference limits. Clinically, these different characteristics are related to discordant results in the diagnosis and prognosis of patients presenting to an emergency department.

Using High-Sensitivity Cardiac Troponin T for Acute Cardiac Care

The recent approval of the fifth-generation cardiac troponin T assay, which has characteristics clinically of a high-sensitivity assay, has led to concern that the problems of increased sensitivity will be greater than the benefits. This will not be the case if cardiology, emergency medicine, and laboratory medicine combine to develop procedures for use of the assay. We advocate sex-specific 99th percentile upper reference limit values of 15 ng/L for men and 10 ng/L for women. We suggest a 2-hour rule-out strategy, including a value less than the 99th percentile upper reference limit and the lack of a change in values of <4 ng/L. Those with values >100 ng/L and or a changing pattern of values ≥10 ng/L are a population much more likely to have acute myocardial infarction. Most of the increment in elevated values will occur not in those with acute coronary problems but in those with primary cardiac disease like heart failure and those with primary noncardiac problems. The former belong on a cardiac service because they are at high risk. The latter should have therapy on the service most apt to provide optimal care for their primary diagnosis, with cardiac consultation as needed.