Abstract
Background We have developed and validated the Renal Activity Index for Lupus (RAIL), a composite score of six urinary biomarkers including neutrophil gelatinase – associated lipocalin (NGAL), monocyte chemoattractant protein-1 (MCP-1/CCL2), kidney injury molecule-1 (KIM-1), ceruloplasmin, adiponectin, and hemopexin) to monitor disease activity. It is critical to establish optimal sample handling conditions and storage prior to widespread clinical deployment and meaningful use in clinical trials. We have previously demonstrated the excellent short-term storage stability of NGAL and KIM-1; here we expand testing to include the other 4 RAIL biomarkers.
Methods Urine was collected from 10 patients enrolled in the SLE Clinical and Research Database (IRB 2008-0635). The urine was then aliquoted and tested under shipping conditions, including freeze/thaw, ambient and longer-term storage (figure 1). MCP-1, Ceruloplasmin, Adiponectin and Hemopexin were assayed by single-plex ELISA assay via commercially available kits. We performed Pearson Correlation Coefficient, Deming regression and Bland-Altman analysis.
Results There was no statistical difference in biomarker concentrations in any of the four biomarkers in any of the experimental conditions. Urinary MCP-1, Adiponectin, Hemopexin and Ceruloplasmin are stable following storage at -80°C for up to 3 months, and at 4° or 25°C up to 48 hours followed by -80° C. In addition, shipping on dry ice or with refrigeration leads to no significant loss of signal. The addition of 1 or 2 additional freeze thaw cycles also did not change mean biomarker levels.
