I have an adopted daughter who is now 1 year old. She was adopted at the age of 6 months. Her birthmother was HIV postive. Child test at birth was positive, but the test at 4 months was negative. Is it at all possible that she may be HIV positive. If so, up to what age will a negative test be accurate.

In adults, testing for HIV antibodies is the most common screening method for HIV infection because virtually 100% of infected individuals are antibody positive. All mothers pass antibodies to their infants during the last 3 months of gestation so all children born at full term to HIV positive moms will test positive for HIV antibodies at birth; it may take up to 18 months to clear the antibodies. For this reason, more specific testing for the virus (also called "DNA or RNA PCR") is recommended for children under 18 months of age. You don't mention which tests were done on your child. The results are a little unusual but could be compatible if the first test was an antibody test and the second was a PCR test. If the test done at 4 months of age was a PCR test, then your child is likely uninfected. You should review the test results with your care provider to be sure.