The Importance of Being Aware of Intrinsic Methods' Limitation in Low-Density Lipoprotein Cholesterol Determination to Correctly Identify Cardiovascular Risk: Is Direct Determination Obtained with the Roche System Systematically Overestimating LDL in Very High-Risk Patients with Triglycerides Concentration of Less than 2.25 mmol/L?

Background: low-density lipoprotein cholesterol (LDL-C) is a strong cardiovascular risk factor, but the methods used to correctly determine it are is still questioned. The aim of this study was to compare the direct determination of LDL-C levels, obtained with the Roche cobas c system, with LDL-C values calculated through Sampson's and Friedewald's equations in very high-risk patients with triglycerides concentrations of less than 2.25 mmol/L (<200 mg/dL).

Methods: in 127 consecutive patients with a recent diagnosis of acute coronary syndrome and triglycerides of less than 2.25 mmol/L, plasma LDL-C was measured directly and calculated with Sampson's and Friedewald's equations before hospital discharge, and the data were compared.

Results: median LDL values obtained with the Friedenwald and Sampson equations and with direct determination were 2.31 (IQR 1.59-3.21), 2.36 (IQR 1.66-3.26) and 2.64 (IQR 1.97-3.65) mmol/L, respectively. Direct measurements were higher by 0.35 and 0.40 mmol/L when compared to the levels calculated with Sampson's or Friedewald's equations, respectively (p < 0.01). The correlation between the two equations was almost perfect (rho 0.997) but decreased when the directly determined data were compared to those calculated with Sampson's equation (rho 0.954) or Friedewald's method (rho 0.939).

Conclusion: direct determination generated higher values of LDL-C concentration through a probable systematic overestimation.