Low-density Lipoprotein Cholesterol Estimation Research Articles

Effect of serum lipoprotein(a) on estimation of low-density lipoprotein cholesterol by the Friedewald formula

The calculation of serum low-density lipoprotein cholesterol (LDL-C) by the Friedewald formula does not account for the cholesterol associated with lipoprotein(a) [Lp(a)]. To quantify the contribution of Lp(a) cholesterol to total serum cholesterol, we measured concentrations of serum Lp(a) by an ELISA and concentrations of other serum lipids and lipoproteins by standard assays in 23 normolipemic women, ages 50-60 years. In measuring serum high-density lipoprotein we found that polyethylene glycol 6000 precipitated > 99.8% of all Lp(a). When serum Lp(a) concentrations were < or = 300 mg/L, 301-600 mg/L, and > 600 mg/L, the uncorrected serum LDL-C was overestimated, respectively, by a mean of 4.1% (n = 7), 8.5% (n = 8), and 21.4% (n = 8). Serum Lp(a) concentrations were positively correlated with percentage overestimation (P < 0.001), but were not correlated with either corrected or uncorrected serum LDL-C. We conclude that the Friedewald formula should be modified to take into account the contribution of Lp(a) cholesterol to total serum cholesterol.

Calculation of Low-Density Lipoprotein Cholesterol

<h3>To the Editor.—</h3> In their article, Leighton et al¹used Système International (SI) units to report their results with the corresponding traditional units in brackets. However, the equation they included in their "Methods" section for the calculation of low-density lipoprotein cholesterol (LDL-C) can be applied only with the latter units.²The correct equation to use with SI units is: LDL-C = Total Cholesterol— (HDL-C + 0.38 × Triglycerides). This error is not uncommon in the American literature.^3-5Authors should be reminded that familiar equations used with traditional units must be adapted before utilization with SI units. By the way, I would like to mention that two recent articles^6,7demonstrated that the original Friedewald equation⁸generally gives a more accurate estimation of LDL-C than the modified version.²

Measured versus calculated LDL-cholesterol in subjects with type 2 diabetes.

Objective:There is a strong positive association between increased low-density lipoprotein cholesterol (LDL-C) and coronary heart disease (CHD). The accuracy of LDL-C estimation is essential and critically important. The aim of present study was to compare calculated LDL-C with direct homogeneous assay in patients with type 2 diabetes.Methods:This observational study was carried out at Baqai Institute of Diabetology and Endocrinology (BIDE) from January 2011 to December 2013. A total of 9620 patients with type 2 diabetes were included in the study. Fasting blood glucose, total Cholesterol, triglyceride, HDL cholesterol and LDL cholesterol were obtained using standard methods. Calculated LDL-C was obtained by Friedewald formula.Results:Mean difference of measured and calculated LDL-C was found to be -0.25, 6.63 and 46.55 mg/dl at triglyceride levels < 150 mg/dl, 150 - 400 mg/dl and ≥ 400 mg/dl, respectively. The result shows that the difference between measured and calculated LDL-C increases as the triglyceride level increases.Conclusions:The findings of our study suggested that calculated LDL-C was lower, as compared to measured LDL-C, which may cause misclassifications that may have an impact on therapeutic decisions in patients with diabetes. Calculated LDL-C may depend on triglyceride levels so LDL-C should be measured by direct assay in routine clinical laboratories.