The acceptance level of HCPs has commonly been in the range 1-100 ppm (1-100 ng/mg product) due to the detection limit of the established analytical methods.[5] Even with these trace levels of HCPs in the final product reaching the patient, it is unknown if specific HCPs might affect protein stability or immunogenicity in the patient.[6][7] If the stability is affected, durability of the active substance in a biopharmaceutical could decrease.