The diagnostic value of blood samples is undisputed, but the sample collection and storage chain is resource-intensive as well as wasteful. A patient must first go to a healthcare unit where a trained nurse obtains a venous blood sample, which is sent to a lab for centrifugal separation of plasma. The sample can then be analysed and/or saved in freezers.

Research conducted at Uppsala University, Sweden, shows that dried blood samples can serve the same diagnostic purpose but in a much more efficient way. Blood proteins remain relatively stable when samples are allowed to dry, suggesting that dried samples could be used for routine health service checks. These could be performed in the fast-growing laboratory service sector, enabling people to have their state of health investigated without engaging medical and health services. The samples could also be used to set up very large-scale biobanks. Healthcare sector costs would decline, more samples could be analysed, and a high proportion of all blood samples taken could be saved.A drop of blood on filter paper for future diagnostics. (Photograph: Johan Björkesten)

The researchers evaluated recently dried blood spots (DBS) as well as others preserved for up to 30 years in biobanks in Sweden and Denmark. These two facilities keep their DBS at different temperatures: the Swedish one at +4°C and the Danish one at −24°C. The samples were used to analyse levels of 92 proteins that are relevant in oncology. Wet plasma samples, kept at −70°C for corresponding periods of time, were also used. In addition, in order to be able to distinguish the effects of the long-term storage, the researchers examined what happens to protein detection as an effect of the drying process.

Protein levels were measured with high precision by proximity extension assay. The drying process has a negligible effect on the proteins and the effect is reproducible, which means that it can be included in calculations.

The use of DBS affords a range of advantages over using “wet” samples. Examples are minimal stress for patients since a tiny, self-administered prick on the finger suffices; costs of collection and storage are low; no highly trained staff are required for the sampling; samples can be sent by letter post; and storage conditions are simple.