Clinical significance of high-density lipoprotein cholesterol in patients with low low-density lipoprotein cholesterol

Objectives We sought to evaluate the significance of high-density lipoprotein cholesterol (HDL-C) in the context of low low-density lipoprotein cholesterol (LDL-C). Background Earlier studies support an inverse correlation between circulating HDL-C and coronary risk in patients with normal or elevated LDL-C. Methods This study involved 4,188 patients attending the Palo Alto Veterans Administration Medical Center or affiliated clinics with LDL-C levels below 60 mg/dl. Outcomes were examined 1 year after the index LDL-C date. The combined primary end point was myocardial injury or hospitalization from ischemic heart disease. The secondary end point was all-cause mortality. Results Mean HDL-C levels (mg/dl) by quartile (Q) were: Q1 28 mg,/dl, Q2 36 mg/dl, Q3 43 mg/dl, and Q4 63 mg/dl. The rate of myocardial injury or hospitalization for ischemic heart disease showed an inverse relationship to HDL-C (adjusted odds ratios: Q1 1.59 [95% confidence interval (CI) 1.16 to 2.19], Q2 1.39 [95% CI 1.01 to 1.92], Q3 1.33 [95% CI 0.96 to 1.84], and Q4 reference) that persisted regardless of statin use or recent myocardial injury. Analyzing HDL-C as a continuous variable revealed a 10% [95% CI 3% to 17%] increase in the combined end point of myocardial injury or hospitalization for ischemic heart disease for every 10-mg/dl decrease in HDL-C. The unadjusted and adjusted incidence of all-cause mortality demonstrated a U-shaped relationship to HDL-C (adjusted odds ratios: Q1 1.13 [95% CI 0.79 to 1.62], Q2 0.97 [95% CI 0.67 to 1.40], Q3 0.74 [95% CI 0.50 to 1.09], and Q4 reference). Conclusions The inverse relationship between HDL-C and coronary risk persists even among patients with LDL-C below 60 mg/dl, although a U-shaped relationship is observed between HDL-C and all-cause mortality.