True 99th centile of high sensitivity cardiac troponin for hospital patients: prospective, observational cohort study?

Abstract

OBJECTIVE
To determine the distribution, and specifically the true 99th centile, of high sensitivity cardiac troponin I
(hs-cTnI) for a whole hospital population by applying the hs-cTnI assay currently used routinely at a large
teaching hospital.

DESIGN
Prospective, observational cohort study.

SETTING
University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom, between 29
June 2017 and 24 August 2017.

PARTICIPANTS
20000 consecutive inpatients and outpatients undergoing blood tests for any clinical reason.
Hs-cTnI concentrations were measured in all study participants and nested for analysis except when the
supervising doctor had requested hs-cTnI for clinical reasons.

MAIN OUTCOME MEASURES
Distribution of hs-cTnI concentrations of all study participants and specifically the 99th centile.

RESULTS
The 99th centile of hs-cTnI for the whole population was 296 ng/L compared with the manufacturer’s
quoted level of 40 ng/L (currently used clinically as the upper limit of normal; ULN). Hs-cTnI
concentrations were greater than 40 ng/L in one in 20 (5.4%, n=1080) of the total population. After
excluding participants diagnosed as having acute myocardial infarction (n=122) and those in whom
hs-cTnI was requested for clinical reasons (n=1707), the 99th centile was 189 ng/L for the remainder
(n=18171). The 99th centile was 563 ng/L for inpatients (n=4759) and 65 ng/L for outpatients
(n=9280). Patients from the emergency department (n=3706) had a 99th centile of 215 ng/L, with 6.07%
(n=225) greater than the recommended ULN. 39.02% (n=48) of all patients from the critical care units
(n=123) and 14.16% (n=67) of all medical inpatients had an hs-cTnI concentration greater than the
recommended ULN.

CONCLUSIONS
Of 20000 consecutive patients undergoing a blood test for any clinical reason at our hospital, one in 20
had an hs-cTnI greater than the recommended ULN. These data highlight the need for clinical staff to
interpret hs-cTnI concentrations carefully, particularly when applying the recommended ULN to diagnose
acute myocardial infarction, in order to avoid misdiagnosis in the absence of an appropriate clinical
presentation.

TRIAL REGISTRATION
Clinicaltrials.gov NCT03047785