Any blood containing HIV and hepatitis or other abnormalities was excluded. The blood was processed, preserved and frozen before it was shipped to the central processing centre in Marburg, Germany. The blood was thawed and pooled together. The fats were removed and the protein levels and pH were adjusted. It was filtered in a sterile environment and the vials were filled to 1.00 ml before being freeze-dried and sealed.
All samples produced have exactly the same composition.
To measure the protein concentrations precisely, some pure proteins were produced and existing WHO reference materials for plasma proteins were used. The resulting CRM exists as an international master calibrator. It has two to five years life but based on current demand, there are enough samples to last at least ten years. In turn, the CRM is used to develop calibrators for national laboratories as well as commercial calibrants with one to two years of life. The measurements performed with equipment calibrated using these are reliable.