Thanks alot. What is the difference between HIV Negative Elisa tests 0.18 and 0.36? was 0.18 2 months ago and now 0.36.please help

Meaningless. These are lab values that express to the lab authorities the validity of the test and do not in any way represent anything of concern to you. These both represent being HIV negative. They are both fully negative and the 'numbers' are meaningless for you to worry about.