Tehran University of Medical Sciences Frontiers in Emergency Medicine 2717-3593 3 3 2019 05 12 e24 e24 Zinat Nadia Hatmi Departmentof Preventive Medicine, Medical School, Tehran University of Medical Sciences, Tehran, Iran / Department of Epidemiology, Centre for Public Health, Medical University of Vienna, Vienna, Austria Nasrin Jalilian Department of Obstetrics and Gynecology, Kermanshah University of Medical Sciences, Kermanshah, Iran Ali Pakravan Institute of National Insurance, Tehran, Iran 2019 05 05 2019 05 11 Introduction: So far, there is no evidence available to demonstrate the relationship between five subgroups of total cholesterol/high density lipoprotein cholesterol (TC/HDL-C) ratio with premature myocardial infarction (MI). Objective: We conducted a case control study to probe more features of the relation between TC/HDL-C ratio and the five subgroups of the ratio with myocardial infarction under 55 years and above it. Method: A hospital based case control study with incident cases was designed. Cases and controls were comprised of 523 under 55-year and 699 above 55-year documented newly diagnosed MI cases, respectively. Standardized clinical and para clinical method were used to ascertain disease and risk factors. Independent sample t-test, Pearson chi square test, Odds ratios and Mantel-Haenszel test and logistic regression analysis conducted to evaluate relationships. Results: This study enrolled 1222 MI cases.  Patients with very low risk category of TC/HDL-C ratio estimated OR=0.18 with 95% confidence interval (CI) (0.04-0.72) for developing MI under 55 years. Patients who had low risk category of TC/HDL-C ratio having OR=0.26 95% CI (0.07-0.89). Low risk and very low risk categories of the TC/HDL-C ratio compare to high risk subgroup of the ratio demonstrate decreased risk of developing MI under 55 years p<0.05. Conclusion: Our study results can be translated as an aggressive treatment for lowering TC/HDL-C ratio in both general population and victims of coronary events. Mitigation of the level of TC/HDL-C ratio from low risk to very low risk category will attenuate the risk of MI under55 years about 8% which is the immediate clinical implication of our findings. https://fem.tums.ac.ir/index.php/fem/article/view/149 https://fem.tums.ac.ir/index.php/fem/article/download/149/176