Evaluation of an Immunoturbidometric Assay for Measurement of Total Adiponectin Concentration in Equine Serum Samples.
BACKGROUND Total adiponectin (TA) is a marker of metabolic health in equids, with values below a critical decision point of < 7.9 μg/mL conferring increased risk of laminitis. OBJECTIVES To evaluate an IT assay to measure serum [TA] in equids and to assess its correlation with [high molecular weight adiponectin] (HMWA) measured by ELISA. METHODS Total serum adiponectin concentrations from 207 adult horses were measured using both an IT assay for TA and HMWA using a previously validated ELISA assay. Data were analyzed using Spearman correlation and Passing-Bablok regression. Intra- and inter-assay precision, linearity, lower limit of quantification (LLoQ), and freeze-thaw stability were assessed for the [TA] assay. RESULTS Mean (range) intra-assay coefficient of variation (CV%) was 2.3% (1.8%-2.8%); inter-assay, across-day CV% was 3.3% (3.25%-3.4%), and across reagent lot CV was 11.7% (9.0%-17.9%). Mean recovery upon dilution was 133.7% (122.6%-140.6%), and LLoQ 1.3 μg/mL. The median CV for 5 freeze-thaw cycles was 3.0% (range 1.0%-3.0%) with a median change in concentration of -11% (range -[9.9-17.1]%). A strong correlation between [TA] and [HMWA] is observed (ρ = 0.90 [95% confidence interval 0.86-0.92], p < 0.001), although in 18% of samples, [HMWA] > [TA]. CONCLUSIONS The turbidimetric immunoassay is sufficiently precise and reliable for measurement of [TA] in equids, especially around the critical decision point, and LLoQ was below the lowest clinical cut-off value. [TA] overall correlated well with [HMWA] in this population, although instances of higher [HMWA] than [TA] were noted at high [HMWA].