Dried blood spots (DBS)--drops of capillary whole blood collected from finger stick--represent a minimally invasive alternative to venipuncture that facilitates the collection of blood samples from research participants in naturalistic, field-based research settings. But the number of validated assays for quantifying biomarkers in DBS samples is relatively low in comparison with serum or plasma. The objective of this review is to discuss the advantages and disadvantages of DBS sampling, and to outline the steps involved in developing and validating an immunoassay for application to DBS samples. These steps include deciding on reagents, preparing calibration and quality control material, evaluating elution protocols, optimizing sample quantity, and assessing multiple aspects of assay performance, including intra- and interassay variation, lower limit of detection, accuracy, stability, and agreement between results from matched DBS and plasma samples. The broader goal of this "how-to" approach is to encourage investigators to validate, implement, and disseminate assay protocols for DBS samples in order to advance field-based research on human biology.
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