# Probabilities of changing rhesus factor

**URL:** <https://boards.straightdope.com/t/probabilities-of-changing-rhesus-factor/212737>\
**Category:** Factual Questions\
**Created:** [November 12, 2003, 1:46am UTC](https://boards.straightdope.com/t/probabilities-of-changing-rhesus-factor/212737 "2003-11-12T01:46:32Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![biddee](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@biddee](https://boards.straightdope.com/u/biddee)\
**Post date:** [November 12, 2003, 1:46am UTC](https://boards.straightdope.com/t/probabilities-of-changing-rhesus-factor/212737/1 "2003-11-12T01:46:32Z")

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Another blood type question caught my eye and I started wondering…my ex boyfriend had O+ blood type. His mother told me that he was tested as a child and again as an adult. About 2 years ago, he was asked to donate blood (his father is a surgeon). When he went to donate, they tested his blood type there in front of all of us and he was O-. Because of the original test, his father asked that it be tested again. Again it was O-.

I have actually heard anectdotal evidence of this happening, but I was wondering what either the science was behind it, or whether the original tests were just bogus and that it is an absolute impossibility.