Quantification of LDL-Cholesterol Corrected for Molar Concentration of Lipoprotein(a)

Purpose: Cholesterol in lipoprotein(a) [Lp(a)-C] is commonly estimated as 30% of the measured Lp(a) mass. However, difficulties in the accurate measurement of Lp(a) mass, along with the inaccuracy of the 30% assumption, produce erroneous values when LDL-C is corrected for Lp(a) [LDL-C_Lp(a)corr]. Our aim was to develop a new formula for LDL-C_Lp(a)corr to reduce this error. Methods: We developed a new formula to calculate Lp(a)-C from the molar measurement of Lp(a), which is Lp(a) nmol/L × 0.077 = Lp(a)-C mg/dL. The calculated Lp(a)-C is subtracted from LDL-C to obtain LDL-C_Lp(a)corr. The results obtained with our novel formula versus the conventional formula were compared in 440 samples from 239 participants enrolled in the BANTING study. Results: With the conventional formula, approximately 7% of samples with low LDL-C resulted in negative LDL-C_Lp(a)corr values. With the new formula, no negative LDL-C_Lp(a)corr values occurred. Among groups with the highest Lp(a)/apoB ratio (p < 0.001) and smaller apolipoprotein(a) isoform size (p < 0.006), LDL-C_Lp(a)corr was significantly underestimated by the conventional formula, which may result in the undertreatment of some patients. Conclusion: The new formula provides more reliable estimates of LDL-C_Lp(a)corr than the conventional formula. Trial registration: ClinicalTrials.gov NCT02739984.