2.3. Assessment of LDL Cholesterol Target Levels According to CVD Risk

LDL cholesterol levels were calculated using the Friedewald equation for participants with serum triglyceride levels less than 400 mg/dL as follows: LDL cholesterol (mg/dL) = total cholesterol − high-density lipoprotein (HDL) cholesterol − (triglyceride/5) [14].

The major risk factors for CVD included five items: (1) men aged ≥ 45 years and women aged ≥ 55 years; (2) systolic blood pressure (SBP) ≥ 140 mmHg and diastolic blood pressure (DBP) ≥ 90 mmHg or current treatment with antihypertensive medications for more than 20 days per month; (3) current smoker; (4) HDL cholesterol level < 40 mg/dL; and (5) family history of premature CVD developing before the age of 55 years in men and before the age of 65 years in women among an individual’s parents and/or siblings. HDL cholesterol ≥ 60 mg/dL was considered as a protective factor for CVD risk [7].

We categorized the participants into four risk groups (low risk, moderate risk, high risk, and very high risk) based on their total CVD risk level. Participants who had no or one CVD risk factor (among the major five risk factors for CVD) were classified into the low-risk group. The moderate-risk group comprised participants with two or more major risk factors for CVD. Participants with diabetes mellitus without signs of target organ damage were classified into the high-risk group. The very high-risk group consisted of (1) participants who had experienced coronary artery disease, ischemic stroke, or transient ischemic attack; (2) patients with diabetes with signs of target organ damage (glomerular filtration rate < 60 mL/min/1.73 m², albuminuria, concurrence of hypertension); or (3) diabetic patients who were current smokers.

The LDL cholesterol management target levels according to each individual’s CVD risk level were set as LDL cholesterol level < 160 mg/dL for the low-risk group, <130 mg/dL for the moderate-risk group, <100 mg/dL for the high-risk group, and <70 mg/dL for the very high-risk group, respectively [7].

Finally, we defined non-achievement of LDL cholesterol target as a higher LDL cholesterol level than the LDL cholesterol management targets based on one’s CVD risk.