Rhesus Negative

Something that I've noticed crops up a lot with alien abductees and possible human/alien hybrids is the Rhesus Negative issue. Essentially, irrespective of whether your individual blood group is A, B, AB or O, the plasma membranes of most people’s red blood cells carry the series of antigens that categorise them as being Rhesus Positive. Those people without this factor are categorised as being Rhesus Negative. Several abduction researchers have commented on the apparently higher proportion of Rhesus Negative people among abductees than in the population as a whole. However, it's not clear whether this is just anecdotal, or whether there's any scientific evidence to back it up. It's also not clear to what extent those who categorise themselves as hybrids, starseeds, indigoes, etc, agree with what the researchers are saying. But in a field where sceptics are often critical, it strikes me that this is an example of something that could be easily tested and might lead to the community being taken more seriously and getting more support.
I would be interested in hearing people's views on this.