Comparison of direct low density lipoprotein cholesterol measurement with the Friedewald formula and alternative formulas

Abstract

Aim: Our aim was to compare the direct enzymatic measurement with four formulas which are used in determining the value of low density lipoprotein cholesterol (LDL-C) levels. Material and methods: A total of 33842 patients’ files were retrospectively reviewed and data was collected. Triglyceride (TG) group 1, 2, 3, 4 and 5 were consisted of TG levels ≤99 mg/dl, 100-199 mg/dl, 200-299 mg/dl, 300-399 mg/dl and ≥ 400 mg/dl, respectively. LDL-Group 1, 2, 3, 4 and 5 were composed of LDL-C≤100 mg/dl, 101-130 mg/dl, 131-160 mg/dl, 160-190 mg/dl and >190 mg/dl, respectively. Results: All formulas tended to undervalue LDL-C concentrations compared to direct method (p<0.001 for all). The Chen formula had higher degree of correlation compared to other formulas. Acceptable result of Friedewald formula was 53.77%, Chen formula was 62.72%, Hattori formula was 24.72, and Anandaraja formula was 45.98%. Bland-Altman plot results showed disagreement of four formulas with significant proportional and systematic bias compared to direct method. There was no agreement of calculated LDL-C with direct LDL-C when the data was subgrouped according to TG levels. No agreement between direct LDL-C and calculated LDL-C was found. Correlation analysis showed moderate to high level of correlation for Friedewald, Chen, and Hattori calculations, whereas Anandaraja formula showed low to moderate correlation. The Friedewald and Anandaraja formulas mostly misclassified LDL-Group 3 subjects, whereas the Chen and Hattori formulas mostly misclassified LDL-Group 4 subjects. Conclusion: The Chen formula might be an acceptable alternative of the Friedewald formula and other formulas.

Keywords

• lipids
• laboratory methods
• cardiology