Discordance of Non-HDL and Directly Measured LDL Cholesterol: Which Lipid Measure is Preferred When Calculated LDL Is Inaccurate?

Objective. To determine if non-HDL cholesterol (N-HDL) and directly measured LDL cholesterol (D-LDL) are clinically equivalent measurements. Patients and Methods. Eighty-one subjects recruited for 2 cholesterol treatment studies had at least 1 complete fasting lipid panel and D-LDL performed simultaneously; 64 had a second assessment after 4 to 6 weeks, resulting in 145 triads of C-LDL, D-LDL, and N-HDL. To directly compare N-HDL to D-LDL and C-LDL, we normalized the N-HDL by subtracting 30 from the N-HDL (N-HDLA). Results. There was significant correlation between N-HDLA, D-LDL, and C-LDL. Correlation was significantly greater between N-HDLA and C-LDL than between N-HDLA and D-LDL. A greater than 20？mg/dL difference between measures was observed more commonly between N-HDLA and D-LDL, 29%, than between C-LDL and N-HDLA, 11% ( ), and C-LDL and D-LDL, 17% ( ). Clinical discordance was most common, and concordance was least common between N-HDL and D-LDL. Conclusions. Our findings suggest that N-HDL cholesterol and D-LDL cholesterol are not clinically equivalent and frequently discordant. As N-HDL may be superior to even C-LDL for predicting events in statin-treated patients, utilizing N-HDL to guide therapy would appear to be preferable to D-LDL when C-LDL is inaccurate. 1. Introduction Calculated low density lipoprotein cholesterol (LDL) is the cornerstone of lipid lowering therapy [1–3]. In certain clinical situations, namely, the fed state or when triglycerides are greater than 400？mg/dL, calculated LDL is inaccurate and the guidelines recommend the use of directly measured LDL cholesterol [1]. We previously reported that calculated and directly measured LDL are not clinically equivalent when targeting ATP III goals with lipid lowering therapy in a significant number of patients [4]. Based on this finding, we recommended that non-HDL cholesterol (N-HDL), an accepted, inexpensive, and guideline-based measure of atherogenic particles, available from the routine lipid panel, replace directly measured LDL (D-LDL) when the calculated LDL (C-LDL) is inaccurate [4]. However, few studies are available comparing the clinical equivalence of calculated LDL, directly measured LDL, and non-HDL cholesterol measurements. Therefore, we evaluated the clinical equivalence of N-HDL and D-LDL which would allow us to determine which lipid measure is more appropriate when C-LDL is inaccurate. 2. Methods Our population consisted of 81 subjects from the Bronx Veterans Affairs Medical Center recruited for 2 research studies from January 2007 through March 2009. The studies