I'm trying to develop a chemi-luminescence based immunoassay for HIV antibody detection. For the purpose I'm using negative as well as positive control as a quality control. Currently, I'm using average of my negative control (NC) which is added to a factor value to get the cut off but the issue with using NC for cutoff calculations gives false positives in certain cases. So, I'm trying to use a PC calibrator for the purpose but the issue here is what exactly I should use that can stay stable for longer time (longer time we can say the time till the expiry of a particular commercial kit, approximately 20% max total reduction in the calibrator value(RLU) is good for me.)
PC calibrator: A control with known desired value used as a control for calculating the cut off for the assay to determine of positive or negative results (For example: PC calibrator with a value of 1.5 (RLU x 10^5) and a factor of 0.150 then the cut off value for that particular assay would be 0.225)