Ethical approval for this prospective case-control study was obtained from the Namık Kemal University Ethical Council of Non-Invasive Clinical Researches (registration number − 2019.185.10.06). Convenient patients above the age of 18 years arriving at the emergency department (ED) of a tertiary care center (a university hospital) between August 1, 2019 and August 1, 2020, and diagnosed with pulmonary embolism based on detection of a thrombus in CTPA were included in this study. Patients who were pregnant, had a history of malignancy, were without CTPA imaging, were forwarded to our center with a confirmed diagnosis, and those who required cardiopulmonary resuscitation were excluded from the study. Healthy volunteers of similar age and gender were selected for the comparison group. Written informed consent was obtained from all patients and healthy volunteers who agreed to participate.
Power analysis was performed to determine the sample size. To obtain 80% power of the analysis at α = 0.05, a sample size of the PE group and the control group was calculated.
When the diagnosis of PE is confirmed, a blood sample of 5 mL was drawn from all included patients and put in red capped tubes. The blood tubes were then centrifuged at 3000 rpm for 15 minutes to separate the serum. The serum samples so obtained were kept at -80°C. After enough sample size was reached, samples were brought to room temperature on the day of analysis, and serum adropin levels were analyzed using the enzyme-linked immunosorbent assay (ELISA) method. Commercially available kits from Sino Gene Clon Biotech Co., Ltd. (catalog no: SG-11594) were used for the study; the kits have intra-assay and inter-assay CV values of < 8% and < 10%, respectively.
CTPA imaging was used as the reference standard in this study owing to the similarity of CTPA image results with pulmonary angiography (gold standard for diagnosing PE) and the ease of access to CTPA in the ED. The imaging was done using GE Bright Speed model 16 detector, and Mx 0.8 cc/kg contrast matter was applied under a pressure of 4 psi.
Additionally, age, sex, presenting complaint, the Geneva score and the Wells’ score, d-dimer, CRP levels, and arterial blood gas analysis for all patients were obtained and saved in their case report forms.
The laboratory technicians evaluating the adropin test was not informed of the final diagnosis of the patients, clinic findings and the CTPA results. The physician assigned to diagnosing the patients in the ED and evaluating the CTPA images had not have inform by the adropin levels, which were not yet studied.
To evaluate the efficacy of adropin, the blood samples from diagnosed PE patients were compared to healthy volunteers with no active complaints and without any history of chronic disease. The treatment planned for any patient was not changed or retarded during the conduct of the study.
Statistical analyses were performed using Statistical Program for the Social Sciences version 18.0 (IBM Inc.) and Analyse-it (Analyse-it Software Ltd). The Kolmogorov-Smirnov test was used to assess the normality of distribution of the adropin levels and PE parameters, and Student’s t-test was used to compare the PE and control groups. Pearson’s chi-squared test was used to determine the relationship between gender and emboli variables, and age and emboli variables. Continuous variables were expressed as either mean ± standard deviation or median (min-max), and the Mann-Whitney U test was used to determine relationships between them. Categorical values were expressed as absolute numbers and percentages. A p-value of < 0.05 was considered statistically significant. Receiver Operating Characteristic (ROC) analysis was specified with 95% confidence interval (95%CI) and Area Under Curve (AUC) values. Cut off was determined according to the highest likelihood ratio.