Leslie J Donato1, Jeffrey W Meeusen2, Sarah M Jenkins3, Stacy J Hartman2, Amy K Saenger4, Nikola A Baumann2, Darci R Block2, Allan S Jaffe5. 1. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 55905, United States. Electronic address: donato.leslie@mayo.edu. 2. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 55905, United States. 3. Department of Health Sciences Research, Mayo Clinic, Rochester, MN, United States. 4. Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN, United States. 5. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 55905, United States; Department of Cardiology, Mayo Clinic, Rochester, MN, United States.
Abstract
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.
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.