If i had chikenpox as a child, why would anyone need to be tested for varicella-zoster ab,igg ? the virus is already in your system. i tested positive

Just good practice: Maybe your doctor tested you because she suspected herpes zoster (shingles), which is a reactivation of VZV, the chickenpox virus. Antibody lab testing is more reliable than patient history in knowing for sure that someone is carrying VZV and that shingles is possible. Not that she didn't trust your history, but still more accurate. Ask the doctor directly if this doesn't seem to explain it.

Now a common thing: Now that a vaccine is available there are less people who will recognize the real disease or have it. Many adults don't think they did & need to check, because it can be deadly in adults. Some mom diagnosed cases were actually something else, but docs never wanted a kid in their office for verification. There are lots of indications for verifying antibody status, one being to save your life.