Deflazacort is a drug that suppresses the immune system, so it is possible that it could slow down the formation of anitbodies to HIV. We do not know how long this effect would last. We would suggest you talk to your healthcare provider about your particular situation. They will be able to advise you if it is safe to stop taking the Deflazacort before testing for HIV, or they might opt to order a test that detects HIV virus instead of antibodies, if this is available in your area.
Let us know if this helps answer your question or if you need more information,