Zero sperm count

Hi, so last week my OH got a zero sperm count through private testing. We were told to go to the gp for bloods and further testing. OH had doctors appointment today through the NHS and was told I need to go for tests first (bloods/vag swabs) then if mine is all ok we will both be referred to a specialist through my doctor for my OH to be tested that way. Just want to see if anyone has a positive story after getting a zero reading and what was the problem? Thank you in advance