Biological variability of lipoprotein-associated phospholipase A₂ activity in healthy individuals

Objectives: Measuring lipoprotein-associated phospholipase A₂ (Lp-PLA₂) activity can aid in identifying individuals at higher risk of coronary heart disease. However, the biological variation of Lp-PLA₂ activity and corresponding reference change value (RCV) is unknown which limits interpretation of results. In this study we aim to define the intra- and inter-individual variability of Lp-PLA₂ activity in a healthy reference population.

Methods: A total of 24 healthy individuals (22-47years of age) were prospectively collected at several time points: daily for five days (after overnight fast), daily for three days (while non-fasting), weekly for four weeks (after overnight fast), and monthly for 6months (after overnight fast). Intra-individual and inter-individual variability was determined. The index of individuality (IoI) and reference change value (RCV) were calculated for each time period.

Results: Variability in Lp-PLA₂ activity was not different in fasting versus non-fasting states and also did not change in daily versus monthly testing. The RCV for monthly Lp-PLA₂ activity was found to be 17%. More than 90% of the variability was attributable to between person differences while analytic variability comprised <9% of the variability and within-person variability was low at <0.7%. The index of individuality for monthly testing was 0.30 CONCLUSIONS: In a healthy population, Lp-PLA₂ activity displays low analytical and within-person variability and higher inter-individual variability. The change required to differentiate a true change in patient status was determined to be 17% for monthly measurements. The between individual variability and corresponding RCV for the activity assay are lower than previously reported results for the Lp-PLA₂ mass assay.