An in-house study was conducted to assess the stability of FLCs in unpreserved serum samples (n=30) stored at 2 to 8°C for up to 7 weeks. For each sample, κ and λ sFLCs were measured at regular intervals. After 3 weeks there was a significant drop in the κ sFLC concentrations (Figure 7.1
). Therefore, it is recommended that samples are stored for a maximum of 21 days at 2 to 8 °C prior to analysis.
A second study assessed the stability of FLCs in unpreserved serum samples stored at -20°C. At each time point, an aliquot was defrosted and κ and λ sFLCs were measured. There was no deterioration in κ or λ sFLC concentrations over 7 months (Figure 7.2
). Therefore, for long term storage of serum samples prior to sFLC analysis, it is recommended that samples are stored frozen at ≤-20°C.
Stability of the Freelite reagent is also an important issue. “Open-vial stability” refers to the shelf-life of the antisera after their first use. This is a minimum of 40 days for the SPAPLUS, but for other instruments the open vial stability may vary due to differences in instrument storage conditions (Chapter 37).