Measuring lipoprotein-associated phospholipase A2 activity in China: Protocol comparison and recalibration

Lp-PLA2 is a novel inflammation marker in cardiovascular disease. While several manufactures have registered Lp-PLA2 activity reagents, few studies have investigated the consistency among these assays. In this study, we compared and recalibrated Lp-PLA2 activity assays.

Serum samples from 110 patients and 140 healthy individuals were collected for method comparison and reference interval validation, respectively. Fresh human serum pools (847 and 442 U/L) were used for recalibration. Lp-PLA2 activity was analyzed using all five assays with a Beckman AU 5800 analyzer. Passing-Bablok regression equations and Bland-Altman plots were used to estimate the relationship and bias among the results. A 2.5% confidence interval (CI) and 97.5% CI were used to establish a laboratory reference interval.

Assay imprecision varied from 0.8%-2.9%, while the overall coincidence rates ranged from 75.5%-98.2%. Passing-Bablok regression shows excellent linear correlation between Evermed and Diasys (R²  = 0.999), while that between Diazyme and Evermed was poor (R²  = 0.846). The R² and correlation coefficient r among assays were 0.846-0.999 and 0.8947-0.9993, respectively. The mean bias percentages ranged from -71.5%-1.6% and -2.0%-11.6% before and after recalibration. As Diazyme and Diasys were not comparable, the Diazyme assay was not recalibrated. The reference intervals determined for Diasys, Evermed, Hengxiao, and Zybio were 184-605, 208-704, 81-328, and 273-696 U/L, respectively.

Our results indicate that recalibration increased assay agreement and also highlight the need for each laboratory to establish its own reference interval for Lp-PLA2 activity.