Received on December 18, 2007
Accepted on April 21, 2008

Informatics and Statistics

Atherosclerosis Risk in Communities (ARIC) Carotid MRI Flow Cytometry Study of Monocyte and Platelet Markers: Intraindividual Variability and Reliability

¹ Collaborative Studies Coordinating Center, University of North Carolina at Chapel Hill, Department of Biostatistics, Chapel Hill, NC
² University of Texas Health Science Center at Houston, Division of Hematology and Vascular Biology Research Center, Houston, TX
³ University of Minnesota, School of Public Health, Division of Epidemiology and Community Health, Minneapolis, MN
⁴ University of Texas Health Science Center at Houston, Human Genetics Center and Institute for Molecular Medicine, Houston, TX

^* To whom correspondence should be addressed. E-mail: diane_catellier{at}unc.edu.

BACKGROUND: Cellular markers help identify different components of a pathological process and may contribute to the diagnosis, prognostic assessment, and management of patients with suspected syndromes. Flow cytometry can be used to accurately assess markers of platelet and leukocyte activation and cellular aggregation in whole blood. To use cell markers as predictors of disease requires that they be measured reliably and show modest within-individual, day-to-day variation.

METHODS: We used whole blood flow cytometry to analyze monocyte and platelet markers in the Atherosclerosis Risk in Communities (ARIC) Carotid MRI study. We estimated laboratory variability using 20 split samples, process variation using replicate blood tubes taken from 112 subjects, and biologic plus process variation using replicate blood samples taken 4–8 weeks apart from 55 people.

RESULTS: For most analytes, the laboratory CV was <10% (mean 3.6%, range 0%–14.5%) and reliability was excellent (75% of analytes had R > 0.90). Reliability coefficients based on repeat-visit data indicated substantial to high repeatability (R > 0.60) for CD14, Toll-like receptor (TLR)-2, CD162, CD61, CD41, CD62P, CD154, and platelet–leukocyte aggregates. In contrast, TLR-4, CD45, myeloperoxidase (MPO), and cyclooxygenase (COX)-2 had slight to moderate repeat visit reliability.

CONCLUSIONS: The high repeatability results for selected platelet and monocyte markers indicate that they can be reliably measured in multicenter studies with delayed sample processing, provided that rigorous standardization of sample collection, shipping, and flow cytometry procedures is applied.