Study Finds ‘Considerable Discordance’ Between Estimated, Direct Measures of LDL-C

Standard cholesterol tests that rely on the Friedewald equation underestimate low-density lipoprotein cholesterol (LDL-C) levels, particularly in cases of high triglycerides, according to a large study published online March 21 in the Journal of the American College of Cardiology. The authors say this discordance may result in the undertreatment of some high-risk patients and they call for additional evaluation in these patients. In this study, researchers examined lipid profiles in 1,310,440 patients (52 percent women) who underwent vertical density spin gradient ultracentrifugation lipid profiling between 2009 and 2011 at Artherotech Diagnostics Lab (Birmingham, Ala.), including 191,333 patients with Friedewald LDL-C less than 70 mg/dl. The researchers found that there were greater differences between Friedewald estimates and direct LDL-C measurements, particularly in patients with lower LDL-C and higher triglyceride levels. When triclycerides were 150 to 199 mg/dl, median direct measures of LDL-C were 9 mg/dl higher than Friedewald estimates, and when triglycerides were 200 to 399 mg/dl, direct measurement was 18.4 mg/dl higher than the estimated LDL-C. “The Friedewald equation tends to underestimate LDL-C most when accuracy is most crucial . . . and therefore additional evaluation is warranted in high-risk patients,” writes lead author Steven Jones, M.D., from Johns Hopkins (Baltimore). For more on how diagnostics are being used to assess cardiovascular risk, please see the Special Focus section on page 8