I see a lot of people talking about struggling with the SPE tests at Biolife, and this document from the FDA seems to say that some type of protein testing is required every 4 months
In addition to the quantitative total protein test performed at each donation, a serum protein electrophoresis, a quantitative immunodiffusion test, or an equivalent test shall be performed every four months. The tests are performed to assess the health of the donor to continue in the program. If the donor's test results are not within the ranges set by the laboratory the donor must be


