The control line is aimed to ensure the user that chromatography has been performed up to the top of the strip. It does not give any indication on the diagnostic itself.

Whenever a signal is observed on the test line (weak or strong), it means that the sample is positive for the pathogen of interest.

In some cases, when the sample is highly positive, the majority of gold conjugate stops at the test line. And only the remaining part migrates to the control line, which explains why the control line could be sometimes weak. If the test line is positive, the test is positive even if the control line is weak or very weak.