False Positive / False Negative

A false positive can fake place under certain medical conditions, etc.  

However, under what medical conditions could a false negative take place?

I've read many things about this on various websites but have not found a definitive answer.

Second question. How does a take home test (Home Access Rapid and Standard) test advertises 99.9% accuracy?  Does the 99.9% include false negatives and false positives?

[LIZZIE LOU]

false negatives occur when testing too early.

[Broadway00000]

Oh, okay.  So pending the person being tested did so past the 3 month mark there would be no such thing as a false negative?

Thanks.

[LIZZIE LOU]

3 months post exposure produces a RELIABLE and CONCLUSIVE result.

[Broadway00000]

Thanks for the info.