First time using opks and I got the wondfo brand since it's a great price and people seem to use it and like it! I completely understand that if the test line is lighter than the control, the result is negative. However the question I have is the back of the package says no test line (only a control line showing) is "invalid". If the test line is blank does that mean the test was faulty? Should you test again with a new strip? Thanks in advance; new to all this! 😊