Blood samples were collected from EPIC participants at recruitment, and these are stored at very low temperature in liquid nitrogen (—196 °C) until they are required for laboratory analysis. Samples were obtained from virtually 100% of participants in each centre except in France and Oxford, where, for logistical reasons, samples were obtained from 33% of participants.
The process for collecting and storing the blood was standardized throughout the seven original participating countries (France, Germany, Greece, Italy, the Netherlands, Spain, and the United Kingdom). A 30 ml sample of blood was obtained from each participant. Plasma, serum, erythrocytes, and buffy coat were separated by centrifugation and aliquoted into 28 0.5 ml plastic straws (12 containing plasma with sodium citrate, 8 with serum, 4 with erythrocytes, 4 with buffy coat). The straws, storage system, and special straw-filling machines were developed for this project by Cryo Bio System and were purchased centrally and distributed to the centres. They are now being used in several large research studies in addition to EPIC.
The samples were then split into two mirror halves of 14 aliquots each. One set of straws (6 with plasma, 4 with serum, 2 with erythrocytes, 2 with buffy coat) was stored locally, and one set was transported to IARC to be stored in liquid nitrogen (at —196 °C) in a central biorepository. Each straw from the same participant is labelled with the participant’s ID and is colour-coded to indicate its contents (red for plasma, yellow for serum, green for erythrocytes, blue for buffy coat).
In Norway, the biological samples were collected in 20 0.5 ml plastic straws. No serum was collected; for 9197 participants, 12 of the 16 plasma samples and 2 of the 4 buffy coat samples were shipped to IARC for storage in the central repository. In Sweden and Denmark, blood samples were stored in 1.5 ml tubes and stored only in local repositories. In Sweden, the samples are kept in freezers (—70 °C), and in Denmark in nitrogen vapour (—150 °C).
The central biobank located at IARC currently contains about 3.8 million straws with blood aliquots from 275 861 EPIC participants, which are stored in 33 liquid nitrogen containers. All 14 straws from the same participant are stored together in a coloured visotube. The visotubes are contained in a goblet (each goblet contains 14 visotubes), which is in turn stored in a canister, placed in a liquid nitrogen tank (http://ibb.iarc.fr/).
All tubes, goblets, and canisters are colour-coded to aid in identifying the samples during the retrieval process. Finally, a Laboratory Information Management System (LIMS) keeps track of details related to a sample’s container, canister, goblet, and the location of the goblet and the canister within each container, to track the stored biological samples of each participant.