4 ms·

It might prevent false positive, but it can lead to false negative. See for example https://www.reddit.com/r/TFABLinePorn/comments/4pxghm/conflicting_pregnancy

• bena 6y ago
  That could happen with any two tests. That second test is really faint. At first I thought "Ok, so they're both negative, so what?" Not to mention, false negatives are far more common than false positives. If you have a false positive, then there's typically some odd health concern with the person.