As of 2009 the number of legal paternity tests that are admissible in court and require a chain of custody was around 400,000. The number of at home paternity tests to legal is somewhere around 1 out of 5 paternity tests being legal so the real number of total paternity tests performed is closer to 2 million tests per year as of 2009 but if the current rate of 64% increase in the number of legal paternity tests performed annually continued, in 2018 that number would be exponentially higher.
When a sibling finds out they have a brother or a sister neither of their parents told them about it can be traumatizing. Everything you think you know about your family is now untrue. It can feel like the ground beneath you is no longer there. Everything you think you know about your family is now untrue.