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

components of a pathological process and may con-tribute to the diagnosis, prognostic assessment, and management of patients with suspected syndromes. Flow cytometry can be used to accurately assess mark-ers of platelet and leukocyte activation and cellular ag-gregation in whole blood. To use cell markers as pre-dictors 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 an-alyzemonocyte and platelet markers in the Atheroscle-rosis Risk in Communities (ARIC) CarotidMRI study. We estimated laboratory variability using 20 split sam-ples, process variation using replicate blood tubes taken from112 subjects, and biologic plus process vari-ation 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). Reliabil-ity 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. I