Questions: %Recovery Acceptance Criteria

Hi All,

I appreciate any input / feedback for the following questions:

  1. What is considered an acceptable percentage recovery from a swab? Is there a rule of thumb, best practice, or guideline for such specification? If so, please indicate the reference. Our SOP indicates acceptance criteria of 70 - 110%. While I was told this range may have come from a PDA guideline, I could not confirm.

  2. What is the difference between “% Recovery” and “Recovery Factor”. I think I know what % Recovery is, but not sure what recovery factor is, how that is determined, and how it is applied.

  3. We recently completed a qualification to qualify personnel to perform swab sampling. In order to qualify, the individuals must demonstrate swab recovery of 70 - 110% (our acceptance criteria) off a coupon surface in triplicates. Unfortunately, the recovery results were consistently below 70%. Several suggestions rose from the failure, including to take the average of the triplicates, and apply a “correction factor”. However, I am not sure what kind of correction factors to consider. I do not believe swab recovery validation was completed in the past. Also, regarding using the average of the results from the triplicates, would that be acceptable if we would only consider results within a given range of the acceptance criteria (i.e. only to take average if say each sample is within of 60-120%, and if the average is between 70-110%, then it passes)?

Thanks in advance for any input. I apologize if my questions and write-up are unclear.

  1. There is no guidance on the minimum % Recovery that is required. In fact there are on ~5 guidances that pertain to cleaning validation.

  2. A recovery factor is the same as a correction factor which is commonly used when the % Recovery drops below a certain minimum that is required by your SOP.

  3. 70% is reasonable while 110% is not (You will have to justify the extra amount recovered. Is your method non-specific?).

  4. A low recovery can be an indication that the target molecule is not fully soluble in the recovery solvent OR that the surface of the material is not inert and absorbs the target molecule (example = silicone gasket).