false positive pregnancy test or false negative pregnancy test

  How can be false positive pregnancy test  or false negative pregnancy  test  results of pregnancy test avoided?

In order to avoid the wrong results and disappointment after pregnancy test we need to follow the test instructions properly.
Furthermore, it’s necessary to take account the following advice:
 Try the several different kinds of pregnant test;
 Take the test again after 2-3 days;
 Take a blood test on chorionic gonadotropin (HCG) in parallel with pregnancy test (with internals of 2-3days).