Biovariability of plasma adiponectin.

BACKGROUND: Adiponectin is a cytokine produced by adipose tissue with insulin sensitising and anti-atherosclerotic effects. Low plasma adiponectin levels are used as a marker of the metabolic syndrome and incipient type 2 diabetes. METHODS: We carried out a series of studies to determine the short- and long-term variability of plasma adiponectin levels, including diurnal and post-prandial changes. These investigations also included examining the effect of frozen storage on plasma adiponectin levels. RESULTS: A nested study in 10 overweight subjects with the metabolic syndrome and 10 age- and sex-matched controls showed intra-subject variation in adiponectin levels over a 30-day period of 12.2% and 18.8%, respectively, equivalent to reference change values of 1.7 and 3.6 microg/mL. In non-obese subjects, plasma adiponectin levels varied minimally over a 15-month period (baseline, 8.3+/-2.9 microg/mL vs. +15 months, 8.2+/-3.0 microg/mL, p=0.95) and showed only minor diurnal and post-prandial changes (pre-meal, 8.2+/-3.0 microg/mL vs. 3 h post-prandial, 8.3+/-3.1 microg/mL, p=0.60). The adiponectin assay had an intra-assay variation of 8.8%, with storage at -30 degrees C for 33 months or three cycles of freezing and thawing having no discernible effect on adiponectin levels. CONCLUSIONS: These results demonstrate that plasma adiponectin levels have relatively low biovariability and that adiponectin can be sampled fasting or non-fasting to provide a reliable marker of insulin resistance and incipient type 2 diabetes.