That question is still open. The process validation of sterilizing grade filters asks for a product bacteria challenge test under process conditions, meaning the maximum pressure conditions during the filtration process. When PUPSIT is used, the pressure of the product or water wetted filter goes up above the Bubble Point, which typically is higher than 50 psi. The question prevails, whether the product bacteria challenge test needs to be performed at that pressure conditions. Having said this, the integrity test phase is very brief, the pressure will be at the 50 psi level only very shortly, whereby the differential pressure during filtration is utilized at a much longer timeframe.