Quantitation of serum free light chains.

under usual artificial light conditions, and storage of unproc-essed whole blood without antico-agulants at room temperature on the bench. Additionally, we tested the effect of multiple freeze-thaw cycles. 25(OH)–vitamin D 3 measurements were performed on a Cobas E601 an-alyzer (Roche), using the vitamin D 3 (25-OH) assay as recommended by the manufacturer. Samples from each storage experiment were analyzed in 1 run after being stored in the freezer at Ϫ20 °C. The interassay CVs for pooled serum analyses (frozen aliquots) were 6.9% at 25.5 nmol/L 25(OH)–vitamin D 3 and 3.2% at 72.5 nmol/L. For the Roche Bone Control we found CVs of 4.8% at 49.8 nmol/L 25(OH)–vitamin D 3 and 4.0% at 97.8 nmol/L. Exposure to 4 freeze-thawing cycles had no important effect on 25(OH)–vitamin D 3 concentrations ; the values for the mean of 8 samples increased 2.6% from the initial values. This small increase can be attributed to evaporation or freeze-drying processes, but we believe there is also a small positive effect due to increased turbidity of the samples after freeze-thawing cycles. A 4.0% decrease in the mean concentration was seen following storage at Ϫ20 °C for up to 2 months. Mean 25(OH)–vitamin D 3 concentrations (n ϭ 8) during storage under these common laboratory conditions are presented in Fig. 1. A mean decrease of 2.3% was noted after 72 h storage of whole blood on the bench at room temperature, and a mean decrease of 3.4% after 24 h and 8.5% after 7 days storage of serum on the bench in daylight. Mean decreases of 4.5% after 3 days and 8.1% after 7 days storage of serum in the dark at room temperature were noted, whereas a mean decrease of 1.8% was observed after 7-day storage of serum in the refrigerator. We found the concentrations of 25(OH)–vitamin D 3 in its natural state bound to vitamin D– binding protein to be very stable at room temperature, even for un-processed whole blood. For either processed or unprocessed samples, delays of several hours before analysis had negligible effects. Even " forgotten " samples or samples received in an unfrozen state appear to be suitable for analysis, because the decreases noted after 3 days under usual laboratory conditions at room temperature were less than the analytical interassay precision. There appears to be no need for serum to be frozen for transport, and whole blood might even be the specimen of …