The comet assay in human biomonitoring: cryopreservation of whole blood and comparison with isolated mononuclear cells

The comet assay is often applied in human biomonitoring. Most of the time the assay is performed with isolated peripheral blood mononuclear cells (PBMC). However, using whole blood instead of isolated cells reduces processing time, and only 20 µl is sufficient for analysis. In this study, a cryopreservation protocol for human whole blood for application in the comet assay was optimised by removing excess plasma before adding freezing medium. Cryopreservation of whole blood samples (n = 30) did not increase the detected level of strand breaks and formamidopyrimidine DNA glycosylase (FPG)-sensitive sites. Although there was no significant correlation with breaks measured in fresh whole blood, strand breaks detected in frozen whole blood were significantly correlated with breaks measured in frozen PBMC (Pearson correlation r = 0.54, P < 0.01). This correlation was however not observed for FPG-sensitive sites. Since we do not yet know the full extent to which cryopreservation might influence the blood cell population, care should be taken to ensure a similar cell type and storage conditions for all samples in one study.