During ARS both CD4 and CD8 may be decreased (they may well be not). CD4 are hit hardest, however CD4/CD8 is often not inverted at this stage (i.e. there are more CD4s than CD8s). Once cytologic immune response kicks in, both of them usually bounce back, but CD8 grow much higher as a rule. CD4s usually do not restore to the original level. That's why the inversion of CD4/CD8 occurs and overtime with the decrease of CD4s the inverted ratio continues to grow.
Having said that, I must stress that no changes in CD4s, CD8s and their ratio can be used to diagnose HIV
and vice-versa they may not occur during actual ARS. I strongly discourage measuring CD4/CD8s as a way of shortcutting regular testing procedures. There are ample means available now to ascertain your HIV