What can a body intake to have an impact on there bloodtype for paternity testing?

Question

I know someone who went after a guy she swore was the father, but the blood test results said otherwise. She swears there was no one else. I want to believe her but can the tests be wrong? or is there something people can do to alter the test?

Answer 1

They are 99.9 percent accurate, so there is a .1 percent chance it is wrong...

Not very likely.

Answer 2

She is probably in denial.

Those test are usually acurate but she can have a lawyer double check the chain of custody or request a second test through the courts.