Positive Human Serum & Plasma
The simplest way to manufacturer a positive control or calibrator is to use recombinant antigens because they allow for consistent supply, lower cost, and reproduceable yield/quality. However, many view recombinant antigens as not truly representing the native antigen and in fact there are cases where recombinant antigens are missing key epitopes found only on the native antigen. In addition, there are many antigens which are still impossible to manufacture recombinantly, requiring manufacturers to use bulk positive serum/plasma in their controls and calibrators.
Most positive plasma is collected in the USA as sourced plasma (in Sodium Citrate anticoagulant) but can be defibrinated on request. A few analytes (Syphilis, HCV, HIV, Chagas, HBsAg, West Nile Virus, Zika) are also available as true serum.