A study by Coley et al. 
demonstrated that κ sFLCs stored at 22°C are only stable for up to 4 days, but their stability is prolonged when stored at lower temperatures. An in-house study was conducted to assess the stability of sFLCs 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
). These findings were confirmed by Coley et al. 
. Therefore, samples should be stored for a maximum of 21 days at 2 to 8°C prior to analysis.
A second study assessed the stability of sFLCs 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.
Gurtner et al.  studied the stability of κ FLCs in CSF. At ambient temperature, κ CSF FLCs were stable for 1 day (5% mean difference from baseline), refrigerated 2 – 8°C for up to 4 days (3%) and frozen at -20°C for up to 28 days (-5%). There was no deterioration in κ FLC concentrations after two free/thaw cycles (3%).
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. Once opened, Freelite reagents may be used for up to three months, providing that when not in use, the reagent vials are stored at 2 – 8°C, securely capped to prevent evaporation (Chapter 37).