Procedures and practices for the validation of bioanalytical methods using dried blood spots: a review

Dried blood spot (DBS) sampling, the collection of whole blood samples on paper, is an emerging technique used for bioanalytical methods. Several analytical challenges, such as possible effects of spotting volume, hematocrit and spot inhomogeneity are identified for these methods, however, no regulatory-based guidelines for the specific validation of DBS-based assays are available hitherto. To date, 68 validation reports concerning methods for the quantitative determination of drugs in human DBS could be traced in the literature, with large differences in the extensiveness of the reported validations. This review aims to present an overview of these published validations. Additionally, the different challenges of DBS-based assays are discussed and recommendations on how to perform validation tests addressing these challenges are provided.