VARIABILITY OF PLASMA IL-6 AND CROSS-LINKED FIBRIN DIMERS OVER TIME IN COMMUNITY-DWELLING ELDERLY SUBJECTS

Because obtaining multiple blood samples from individuals involved in epidemiologic studies is difficult, conclusions must be drawn on the b asis of one or two samples. In this study, the authors attempted to de termine the variability of two plasma markers over time, namely IL-6 l evels and crosslinked fibrin degradation products (D-Dimers), in 16 el derly community-dwelling individuals. The study group included both me n and women and black and white subjects (four in each group). Eight b lood samples were obtained from each subject over a period of 36 days. Blood was separated within 1 hour after collection and aliquots of pl asma were stored at -70 degrees C until all samples were collected. Al l samples from an individual were analyzed at one time. IL-6 and D-Dim ers were measured by commercially available ELISA kits. The variabilit y in the levels of plasma IL-6 and D-Dimers was assessed by means of i ntra-class correlation coefficient (ICC). The estimates of the ICCs fo r one measurement of IL-6 and D-Dimers were .87 and .86, respectively. Reliability values of this magnitude indicate excellent reproducibili ty in the measurement. These values indicate that obtaining a single s ample from a subject is fairly representative of that individual's IL- 6 and D-Dimer levels over an extended period of time.