Sample stability of autoantibodies: A tool for laboratory quality initiatives

Serum autoantibody measurement aids in diagnosing and monitoring various autoimmune conditions. Defining autoantibody stability limits can improve laboratory process quality. Here, we define short-term stability in a refrigerator, long-term stability in a freezer, and the effect of freeze–thaw cycles to improve autoantibody testing procedures. Seventy-nine residual serum samples were used to assess the stability of 11 autoantibodies (anti-dsDNA, anti-Ro52, anti-Ro60, anti-SSB, anti-RNP, anti-Sm, anti-aCL-IgG, anti-tTG-IgA, anti-tTG-IgG, anti-DGP-IgA, anti-DGP-IgG) and two screening assays (CTD screen, ENA7 screen) on the BIO-FLASH (Inova Diagnostics). Three storage conditions were assessed: 8 weeks at 2–8 °C, 12 months at −30 °C, and 6 freeze (−30 °C)-thaw cycles. The maximum permissible instability (MPI) for each autoantibody was set as 2x %CV, calculated as the weighted average CV from cumulative QC data over the study period. By considering both mean percent difference (MPD) and mean absolute relative difference (MARD), all autoantibodies were stable for up to 8 weeks stored at 2–8 °C, except for CTD screen and anti-dsDNA. All autoantibodies were stable for up to 12 months stored at −30 °C, except ENA screen, anti-dsDNA, anti-DGP-IgA, anti-cardiolipin, and CTD screen. Lastly, all autoantibodies were stable for up to 6 freeze(−30 °C)-thaw cycles, except anti-RNP, anti-Ro60, anti-cardiolipin and anti-dsDNA. It is important to develop laboratory procedures derived from evidence-based stability limits. This study will aid laboratories in undertaking quality assurance and improvement initiatives to enhance autoantibody testing by ensuring appropriate storage conditions that consider defined sample stability limits.