In this study, a new, non-invasive method for diagnosis of pulmonary embolism (PE) will be tested.

In pre-clinical studies, the investigators have identified 151 putative biomarkers for pulmonary embolism in the exhaled breath, and several of these were also found in a first in-human clinical study what the investigators performed in 2019-2020 (DOI 10.1088/1752-7163/ad0aaa). These biomarkers need consolidation in a clinical setting using an updated collection device and proteomic analysis platform before development of a prototype and further test of this new diagnostic method.

The study will compare the protein profiles of exhaled breath from patients admitted to the Emergency Care Center with suspected pulmonary embolism and controls with same age (within a range of 10 years) and gender. The main-outcome (i.e., means of the relative amounts of specific proteins in the exhaled breath samples) will be compared by unpaired t-tests after assessment of normality and standard deviations within the two groups (PE patients and controls). Furthermore, sensitivity and specificity will be calculated for relevant proteins. The results from analysis of exhaled breath samples from the patients and controls will be compared with results from the porcine model and the first clinical study to confirm and reduce the number of putative biomarkers for PE.

Blood samples (i.e. excess plasma from routine blood samples drawn as a part of routine diagnostic work-up) from the study participants will be stored for standardization of the putative markers and verification and supplementing analysis of the exhaled breath markers. In order to qualify the most suitable markers and substrates for standardization, the analysis of the exhaled breath samples must be completed before the blood samples can be analyzed. Only biochemical, no genetic analysis will be conducted.

PE patients:

• Admitted to the Emergency Care Center with suspected PE
• Are conscious and able to understand the given study information.
• Possess legal capacity.
• Age above 18 years.
• Informed, signed consent is obtained.
• Clinically stable, which is defined as patients with stable blood pressure and not in need for other treatments.
• No need for organ support, which comprises need for vasopressors or inotropes, mechanical ventilation, extra corporal circulation, or renal replacement therapy.
• In subjects, where the PE diagnosis is rejected after diagnostic work-up will be included in as clinical controls

Healthy controls:

The healthy age- and gender matched controls will be recruited as a:

• Random sample from the background population who wants to participate voluntarily on a first come, first served basis. They will be recruited from a hospital setting by using posters and by a social media campaign.

Inclusion criteria for healthy controls:

• Same gender and age (within a 10-year range) as an included PE patient.
• Are conscious and able to understand the given study information.
• Possess legal capacity.
• Age above 18 years.
• Informed, signed consent is obtained.

Exclusion criteria for both PE patients and controls:

• Active malignant disease (i.e., ongoing anti-cancer therapy or palliation).
• Current smokers.

It is expected that 30 patients with confirmed PE, 30 patients with suspected PE, but where diagnostic work-up did not confirm PE and 30 healthy controls will be included in the study over a one-year period.