HBcAB IgM and IgG

I have a question regarding the above tests, HBcAB IgM and IgG.

I just recently had a baby. At the beginning of the pregnancy, my Hep B screenings came back negative. While at this point, I can only confirm that the HBsAG was negative in October 2000,(I don't know yet whether a full panel was ordered) I know for a fact that 5 years ago I was negative to all as I was tested when pregnant with my daughter.

When I submitted my baby's cord blood for storage, the company required my blood be tested. I just got a letter last night that the HBcAB IgM and IgG came back repeatedly reactive. The letter also stated that this result could be "falsely reactive" or be a "false positive".

Given that I've tested negative while in a monogomas relationship *and* fall into *none* of the high risk groups (unless you can pick it up from a toilet seat), what can cause false results? My blood was taken while I was on an IV penicillin drip due to my son being a bit premature. Could antibiotics mess up the results?

Thanks for any help here.

Linda