Sample stability of autoantibodies: A tool for laboratory quality initiatives.

ABSTRACT

OBJECTIVES: 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. DESIGN AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.