Adiponectin: Stability in Plasma over 36 Hours and Within-Person Variation over 1 Year

Adiponectin (Arcp30, AdipoQ, apM1, or GBP28), a novel 247-amino acid peptide, is secreted predominantly by adipocytes and accounts for ∼0.05% of total serum proteins (1)(2)(3)(4). It is induced early in adipocyte differentiation (1), consists of an N-terminal collagenous and a C-terminal globular domain, and shares homology to subunits of complement factor C1q (1)(3). Adiponectin expression is reduced in obesity and type 2 diabetes, and plasma concentrations of adiponectin are inversely related to body weight and insulin concentrations (5)(6)(7)(8). Treatment with adiponectin improves insulin sensitivity in mouse models of insulin resistance (9)(10), and in adiponectin knockout mice, adiponectin substitution can reverse diet-induced insulin resistance (11). Adiponectin is also inversely associated with other traditional cardiovascular risk factors, such as blood pressure, heart rate, total cholesterol, LDL-cholesterol, and triglycerides (12)(13). In addition, recent studies suggest that it may have antiatherogenic and antiinflammatory properties (14)(15)(16)(17)(18)(19). Adiponectin may therefore be an important blood biomarker to assess in large-scale epidemiologic studies of several chronic diseases. To gain a reliable risk estimate with a single blood measurement, the within-person variability over time should be small compared with the between-person variability (20). In addition, the stability of a valid biological marker should not be substantially affected by length of storage or temperature (21)(22)(23)(24)(25). Ideally, serum or plasma from whole blood should be separated immediately and stored in deep freeze. In large epidemiologic studies, however, blood specimens are often collected at different times and locations and transported on ice over several hours or days to central laboratories for processing and storage. The aims of the present study were to evaluate the stability of …