Need advice please

Not sure if this is the right place to post this but
Is there any parents out there with children who have hearing impairment or are deaf?
My son is 17 months old and I'm a little concerned about his hearing we talk to him he doesn't acknowledge it, we can shout him and he doesn't turn round we tried a little test where we went behind him and raised our voices and there was no surprise it's like he can't hear us just need some advice on what to do and how to diagnose this. Thankyou xxx