Let's say your donor has a positive RPR, and due to whatever circumstance you want to insert here, you can't do confirm testing, maybe the sample broke.

How long do you defer for? Or do you have a different policy?

12 month deferral.

Reference: FDA Recommendations for Donor Deferral 12/12/1991

Subject: Clarification of FDA Recommendations for donor Deferral and Product Distribution Based on the Results of Syphilis Testing

FDA's Final Rule: "Requirements for Testing Human Blood Donors for Evidence of Infection due to Communicable Disease Agents" June 11, 2001 (66 FR 31146) i

June 2003 FDA Guidance for Industry (appears to still be in DRAFT form) Revised Recommendations for donor and Product Management Based on Screening Tests for Syphilis.

Robin Biswas, M.D, (FDA) is an excellent resource for questions on infectious disease testing (301-827-3011)