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The OUT-ACS study

Pre-hospital One-hoUr Troponin in a low-prevalence population of Acute Coronary Syndrome: OUT-ACS study

About the project

Due to the Norwegian gatekeeping system, many patients with acute chest pain seek a primary care physician for a consult. The acute myocardial infarction (AMI) diagnosis is challenging in the prehospital emergency setting due to less sensitive diagnostic tests. Hence, many patients with chest pain are sent on to hospitals for further diagnostic assessment.


We aimed to validate a new diagnostic algorithm for high-sensitivity troponin T (hs-cTnT), where two troponin samples are drawn only 1-hour apart. This new 0/1-hour algorithm is thoroughly validated for patients in hospital, but a validation of the algorithm in a low-prevalence population remains. Therefore, we aimed to validate the 0/1-hour algorithm for hs-cTnT in a low-prevalence population for ACS by applying the algorithm in a primary care emergency setting.


During the enrolment period (Nov. 2016 - Oct. 2018) 1711 patients were included in the study at Oslo Accident and Emergency Outpatient Clinic (OAEOC). Patients in need of further tests, but not immediate hospitalisation, were offered prehospital hs-cTnT sampling at the OAEOCs observation unit. Hs-cTnT were collected at 0, 1 and 4 hours (control sample) from all participants.

As many as 76.6 % (1311/1711) patients hade AMI ruled out by the 0/1-hour algorithm, with a high diagnostic safety (sensitivity 98.4 %, negative predictive value 99.6 %), and this group also had a very low incident rate for AMI or death the following 90-days (0.3 %).

The 0/1-hour algorithm for hs-cTnT, therefore, seems safe, efficient and applicable for an accelerated assessment of patients with non-specific chest pain in a primary care emergency setting.


The project is run by PhD candidate Tonje R. Johannessen at the Department of General Practice at the Institute of Health and Society, UiO. The project is a collaboration with the research group Myocardial Ischemia at the Department of Cardiology, Oslo University Hospital Ullevaal, and the OAEOC (City of Oslo Health Agency).

The OUT-ACS study is a single-centre, observational, prospective, diagnostic cohort study-

The project started in January 2016, with patient enrolment period from 2016-2018. The project was expanded to a PhD project in 2018, with the planned completion during the spring of 2022


  • Sub-project 1: Comparison of a prehospital single high-sensitivity cardiac Troponin T measurement with the HEART score for rapid rule-out of acute myocardial infarction
    • As many of the patients had symptom duration of more than 3 hours prior blood draw, it was of interest to investigate how many of these who could be triaged by a single hs-cTnT (0-hour sample alone); conducted as a prospective sub-analysis of the main study.
    • In addition, we aimed to investigate whether the well-validated risk assessment tool the HEART-score had addition diagnostic value in the clinical assessment of these patients at the prehospital clinic. (Retrospective calculation of the HEART score for all included patients).
  • Sub-project 2: Ruling out acute myocardial infarction in low-risk patients in a primary care emergency setting: a cost-effectiveness analysis
    • In this second sub-study, we aim to compare both costs and health benefits by assessing the majority of patients with low-risk of acute coronary syndrome at a primary care emergency clinic rather than admitting them to hospital for further assessment.


The Norwegian Research Fund for General Practice, the Norwegian Committee on Research in General Practice and the Norwegian Medical Association's Fund for Quality Improvement and Patient Safety.

Project start and finish:

January 2016 – April 2022

Selected publications

Johannessen, Tonje R.; Vallersnes, Odd Martin; Halvorsen, Sigrun; Larstorp, Anne Cecilie Kjeldsen; Mdala, Ibrahimu & Atar, Dan (2020). Pre-hospital One-Hour Troponin in a Low-Prevalence Population of Acute Coronary Syndrome: OUT-ACS study. Open heart.  ISSN 2053-3624.  7, s e001296 . doi: 10.1136/openhrt-2020-001296

Published Sep. 3, 2020 9:11 AM - Last modified Sep. 3, 2020 9:16 AM