Concordance of Lipoprotein(a) measurements in mg/dL and nmol/L: Insights from the Lp(a)HORIZON trial.

BACKGROUND AND AIM: Challenges in measurement standardization have complicated both research and clinical care. We assessed the concordance of Lp(a) concentration measured in mg/dL and nmol/L using the Roche Tina-quant Lipoprotein(a) Gen 2 mass and molarity Assay™ with values calculated using two published conversion methods in the Lp(a)HORIZON screening program.

METHODS

Lp(a) concentrations were analyzed from 14,247 screened patients for the Lp(a) HORIZON trial. Of those, 13,666 had Lp(a) measurement in both mg/dL and nmol/L. Agreement between directly measured Lp(a) nmol/L values and nmol/L values converted from mg/dL using two published conversion methods - the Copenhagen General Population Study (CGPS) formula and the until recently widely used conversion factor of 2.5 - was assessed. The accuracy of conversion formula was evaluated by comparing converted nmol/L values with measured nmol/L values, using Bland-Altman plots, and by examining concordance with the Lp(a)HORIZON trial selection thresholds (70 mg/dL and 90 mg/dL).

RESULTS

Overall, the CGPS formula showed moderately greater agreement with observed nmol/L measurements (Mean Absolute Error (MAE) = 16.95, Normalized Root Mean Squared Error (NRMSE) = 0.21) compared with the conversion factor of 2.5 (MAE = 42.30, NRMSE = 0.44). For the CGPS and conversion factor of 2.5, the accuracy between directly measured and converted values for selection thresholds used in the Lp(a)HORIZON trial was 97% and 92% at the 70 mg/dL, and 94% and 85% at 90 mg/dL thresholds, respectively.

CONCLUSIONS

The CGPS conversion formula showed a better agreement with measured Lp(a) values and more accurately reproduced the Lp(a)HORIZON selection thresholds than the conversion factor of 2.5.