Final answer:
The absence of a blue line in the control area of a urine pregnancy test means that the test is invalid and must be repeated for accurate results.
Step-by-step explanation:
If a blue line did not appear in the control area of a urine pregnancy test, this indicates that the test is invalid. The control line in a lateral-flow pregnancy test is critical in validating that the test has been performed correctly. Without the appearance of a control line, neither a positive nor a negative result can be determined. It is simply an indication that the test did not work as intended, and it would be necessary to repeat the test with a new strip to obtain a valid result. It does not indicate whether the person is pregnant or not.