Is it considered cheating and forbidden for a female doctor to issue a lab test result indicating the presence of a microbe, even though the test shows its absence due to the low quality of the chemicals, while charging the normal fee?

You are obligated to inform the person requesting the analysis about the inefficiency of the materials if you know they are inefficient. You must also inform them about the inaccuracy of the result after the analysis if it is inaccurate, based on your knowledge of the symptoms. If you do this, there is no sin upon you, and the fee for the analysis is permissible for you.