We enrolled 207 blood donors subjects in the blood bank department in the Tahar Sfar University Hospital of Mahdia as controls in this study. Consecutive patients complaining of chest pain who underwent invasive coronary angiography for the diagnosis of CAD. A total of 310 CAD patients recruited from the Department of Cardiology, University Hospital (Monastir, Tunisia) showed by angiography at least one coronary stenosis of more than 50% of the luminal diameter that were included in the study. We followed the methods of Bouzidi N et al. 2020 [10].

The diagnosis of ACS was based on the guidelines of the European Society of Cardiology (ESC) [11]. NSTEMI-Acute coronary syndrome (ACS) included NSTEMI and UA. NSTEMI was defined as elevated cardiac troponin I (cTnI) values without new ST elevation on electrocardiogram with ischemic symptoms. UA was defined as having newly developed and accelerated chest symptoms on exertion or rest angina without the detection of signifcant cTnI increase. STEMI was defined as a persistant electrocardiographic ST-segment elevation associated to high levels of cTnI after chest pain symptoms (> 20 min).

Chronic lung disease, liver disease, kidney disease, concomitant inflammatory diseases such as infections and autoimmune disorders, or malignancy were excluded. The study protocol complied with the Declaration of Helsinki, and this study protocol was reviewed and approved by the National Committee for Medical and Research Ethics of Farhat Hached University Hospital (Sousse, Tunisia). Written informed consent was obtained from each subject.

Coronary angiographic data were collected from patient catheterization laboratory records and reviewed independently by interventional cardiologists. The severity of CAD was ascertained by the degree of epicardial coronary artery stenosis and was classified as previously published guidelines, as moderate (50–70% stenosis), and severe (> 70% stenosis) and multivessel disease extent [1, 2 or 3-vessel disease stenosis (> 50%)]. Accordingly, patients were categorized as having one or multi-vessel disease. Multi-vessel CAD was confirmed when at least two of the major coronary arteries had significant atherosclerosis [1].

Coronary lesion severity was assessed in each patient by the Gensini Score (GS) [12], which was calculated by scoring each atherosclerotic lesion according to the degree of coronary artery luminal narrowing and the location of the lesion. The total score was calculated as a sum of the product of the stenosis and location score of each affected lesion.

In this scoring system, 0 indicates no abnormality, 1 represents stenosis of ≤ 25%, 2 represents stenosis of 26–50%, 4 represents stenosis of 51–75%, 16 represents stenosis of 76%–99%, and 32 represents complete occlusion. The score is then multiplied by different factors according to the functional significance of the coronary artery. The evaluation of each segment was performed by multiplying the scores by 5 for the left main trunk, by 2.5 for the proximal left anterior descending (LAD) branch, by 1.5 for the middle LAD, by 1 for the distal LAD, by 1 for the first diagonal branch, by 0.5 for the second diagonal branch, by 2.5 for the proximal LCx, by 1 for the distal LCx and posterior descending branch, and by 0.5 for the posterior branch, while the RCA was performed by multiplying the scores by 1 for the proximal, middle and distal RCA and the posterior descending branch, and by 0.5 for the posterior branch. The final score was calculated by adding the scores of each segment. The patients were then divided according to the median of the total score (GS = 40) [12].

Serum interleukin-6 (IL-6) levels were measured by electrochemiluminescence immunoassay (ECLIA) using a Cobas E601 analyzer (Roche Diagnostics, Germany).

Serum samples were collected from study participants immediately upon admission, and stored in aliquots at -80 °C until use. Triglycerides (TG), total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), hsCRP, glucose, urae, creatinine, creatine phosphokinase (CPK) and creatine kinase (CK)-MB isoforms were measured using an analyser (Cobas Integra 600, Roche Diagnostic, Germany) for patients upon admission. Low density lipoprotein-cholesterol (LDL-C) was estimated by the Friedewald equation) [10].

Data were analyzed using Statistical Package for the Social Sciences (SPSS, version 23.0). Continuous variables were described as mean ± standard deviation (SD) for normally distributed data or medians (minimum—maximum) for non-normally distributed data, as appropriate. Categorical data were summarized as frequencies or percentages. IL-6 was log transformed before analyses because its non-normally distribution. Differences in quantitative parameters between groups were performed using independent-samples T test or Mann–Whitney U test, as appropriate. The predictive values of different biomarkers for the presence of CAD and evaluating infarct size were determined by constructing receiver operating characteristic (ROC) curves and the area under the curve (AUC) was calculated. p value < 0.05 were considered as significant. The cut-off value was determined using the Youden index = maximum (sensitivity + specificity – 1) [12].