On August 27, 2015 FDA issued a guidance titled “Class II Special Controls Guideline Document: Toxin Gene Amplification Assays for the Detection of Clostridium difficile”. This guidance refers to software information required in a premarket submission. In addition to repeating information inthe general software submission guidance it indicates most IVDs of this type are moderate level of concern but the level of concern should be determined prior to mitigation. It also states “You must clearly describe how raw signals are converted into a result including adjustment to the background signal for normalization, if applicable.” It also states “Before beginning clinical studies, the configuration of the hardware and software components must be very similar or identical to the final version of the device. A risk assessment must be performed if any significant changes are made to the hardware or software after the completion of the clinical studies and before the clearance and distribution of the device.”.