Supposedly the test can detect the presence of another person's blood in the test blood sample.

I don't know how this test is conducted, but I might do a little bit of digging around to find out.

My semi-educated guess is it would either detect DNA from another person's blood (via a PCR-type reaction) or detect antibodies the test subject generated against non-self proteins in the blood (via an ELISA).

Either way it would be looking for a very small signal in a very large background. Such tests are very tricky, prone to false positives and highly susceptible to operator error.

It would be a tragedy if a man's reputation and career were ruined on account of a test with questionable reliability.

I'm not saying it couldn't have happened; I'm saying that I'm not convinced yet.

Just my 2 cents.