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

Mamas

Abstract

Objective
Clinicians use the cardiac troponin (cTn) assay to aid in the diagnosis of an acute myocardial infarction (AMI). Each assay manufacturer provides the 99th percentile for cTn levels in a group of healthy individuals, and this level is taken as the upper limit of normal (ULN). The objective of this study was to determine the distribution, and specifically the true 99th percentile, for the whole hospital population, using the cTn assay currently employed routinely at our institution.

Design
Prospective study of 20,000 consecutive patients undergoing blood sampling for any reason at a large teaching hospital. Hs-cTnI concentrations (Beckman Coulter Access AccuTnI+3 assay) were nested for analysis in all cases except those in whom the supervising physician had requested hs-cTnI for clinical reasons.

Setting
University Hospital Southampton NHS Trust (UHS).

Participants
20,000 consecutive individuals, inpatient or outpatient, undergoing blood tests at UHS for any clinical reason.

Main outcome measures

Distribution of hs-cTnI concentrations of all study patients, and specifically the 99th percentile.

Results
The 99th percentile of hs-cTnI for the whole population (n=20,000) was 296 ng/L, compared to a manufacturer quoted 99th percentile of 40 ng/L (currently used clinically as the ULN). In 1 in 20 (5.4%, n=1080) of the total population hs-cTnI concentrations were above 40 ng/L. After exclusion of individuals diagnosed with an acute myocardial infarction (AMI) (n=122), or those in whom troponin was requested (n=1707), the 99th percentile for the remainder (n=18,171) was 189 ng/L. The 99th percentile for inpatients (n=4759) and outpatients (n=9280) was 563 ng/L and 65 ng/L, respectively. Patients from the emergency department (n=3706) had a 99th percentile of 215 ng/L, with 6.1% (n=225) above the quoted ULN. 39.02% (n=48) of all individuals from the critical care units (n=123) and 14.16% (n=67) of all medical inpatients had a hs-cTnI concentration above the quoted ULN.

Conclusions
In 20,000 consecutive patients undergoing a blood test for any reason at this hospital 1 in 20 have a hs-cTnI above the supplied ULN. These data highlight the need for clinical staff to interpret hs-cTnI concentrations carefully, particularly when applying the supplied ULN to diagnose AMI. The use of hscTnI to diagnose AMI in any patient could lead to misdiagnosis in the absence of an appropriate clinical presentation

Citation

Mamas. (2019). True 99th centile of high sensitivity cardiac troponin for hospital patients: prospective, observational cohort study. BMJ, https://doi.org/10.1136/bmj.l729

• Acceptance Date: Jan 28, 2019
• Publication Date: Mar 13, 2019
• Journal: British Medical Journal
• Print ISSN: 0959-8138
• Publisher: BMJ Publishing Group
• DOI: https://doi.org/10.1136/bmj.l729
• Keywords: myocardial infarction
• Publisher URL: http://doi.org/10.1136/bmj.l729