Received on June 21, 2007
Accepted on October 25, 2007

Lipids, Lipoproteins, and Cardiovascular Risk Factors

Variability of Serial Lipoprotein-Associated Phospholipase A₂ Measurements in Post–Myocardial Infarction Patients: Results from the AIRGENE Study Center Augsburg

¹ Department of Internal Medicine II—Cardiology, University of Ulm Medical Center, Ulm, Germany
² Ludwig-Maximilians-University Munich, Department of Statistics, Munich, Germany; National Research Center for Environment and Health, Institute of Epidemiology, Neuherberg, Germany
³ National Research Center for Environment and Health, Institute of Epidemiology, Neuherberg, Germany

^* To whom correspondence should be addressed. E-mail: wolfgang.koenig{at}uniklinik-ulm.de.

BACKGROUND: Of the numerous emerging biomarkers for coronary heart disease (CHD), lipoprotein-associated phospholipase A₂ (Lp-PLA₂), an enzyme involved in lipid metabolism and inflammatory pathways, seems to be a promising candidate. Implementation of Lp-PLA₂ measurement into clinical practice, however, requires data on the reliability of such measurements.

METHODS: We measured Lp-PLA₂ concentrations by ELISA in blood samples drawn from 200 post–myocardial infarction patients (39–76 years) at 6 monthly intervals between May 2003 and February 2004, for a total of 1143 samples. We estimated analytical, within-individual, and between-individual variation, the critical difference, and the intraclass correlation coefficient of reliability (ICC) to assess the reliability of serial Lp-PLA₂ measurements.

RESULTS: The mean (SD) plasma Lp-PLA₂ concentration for the study participants was 188.7 (41.8) µg/L, with no significant difference between men and women. The analytical CV for Lp-PLA₂ was 4.4%, the within-individual biological CV was 15%, and the between-individual CV was 22%. The ICC was 0.66. An important part of the total variation in plasma Lp-PLA₂ concentration was explained by the between-individual variation (as a percentage of the total variance, 66.1%), whereas the within-individual variance was 31.3%. The analytical variance was as low as 2.6%.

CONCLUSIONS: Between-individual variation in Lp-PLA₂ concentration was substantially greater than within-individual variation. In general, our data demonstrate considerable stability and good reproducibility of serial Lp-PLA₂ measurements, results that compared favorably with those for the more commonly measured lipid markers.