We received this question earlier by e-mail and it is something that can cause confusion.
The C line or control line on a drug test kit is usually very strong and dark however the T line (test line ) may vary considerably in colour and darkness from test to test and also on different drug test membranes, within the same drug testing kit. This is quite common and is of no significance when interpreting the result of the test.
As long as the T line is clearly visible within the specified time then the result is a negative result i.e. no drug detected. The T line does not need to be as dark as the control line and in fact often is not. On the multi panel urine drug test kit above, you can see that the intensity of the T line varies on the different strips although the control line remains fairly consistent.
We are also often asked can any conclusion be drawn if the T line is faint and does this mean there might be low levels of drugs present. The answer to this is no. The faintness of the T line is not of any significance and is still a negative i.e. clear or pass result.