▁and ▁commonly ▁acquired ▁in fe ctions , ▁quant ification ▁of ▁Ig G ▁sub classes ▁ ▁Test s ▁for ▁ph ag ocy te ▁function : ▁reduction ▁of ▁nit ro ▁blue ▁t et raz ol ium ▁ch lor ide , ▁ass ays ▁of ▁chem ot axis , ▁b acter ic idal ▁activity . ▁ ▁Due ▁to ▁the ▁r ar ity ▁of ▁many ▁primary ▁imm un ode fic ien cies , ▁many ▁of ▁the ▁above ▁tests ▁are ▁highly ▁special ised ▁and ▁tend ▁to ▁be ▁performed ▁in ▁research ▁labor ator ies . ▁ ▁C riteria ▁for ▁diagn osis ▁were ▁agreed ▁in ▁ 1 9 9 9 . ▁For ▁instance , ▁an ▁ant ib ody ▁def ic iency ▁can ▁be ▁diagn osed ▁in ▁the ▁presence ▁of ▁low ▁imm un og lob ul ins , ▁rec urrent ▁in fe ctions ▁and ▁failure ▁of ▁the ▁development ▁of ▁ant ib od ies ▁on ▁expos ure ▁to ▁ant ig ens . ▁The ▁ 1 9 9 9 ▁criteria ▁also ▁distinguish ▁between ▁" def init ive ", ▁" prob able " ▁and ▁" possible " ▁in ▁the ▁diagn osis ▁of ▁primary ▁imm un ode fic iency . ▁" Def init ive " ▁diagn osis ▁is ▁made ▁when ▁it ▁is ▁likely ▁that ▁in ▁ 2 0 ▁years , ▁the ▁patient ▁has ▁a ▁> 9 8 % ▁chance ▁of ▁the ▁same ▁diagn osis ▁being ▁made ; ▁this ▁level ▁of ▁diagn osis ▁is ▁achiev able ▁with ▁the ▁detection ▁of ▁a ▁gen etic ▁mut ation ▁or ▁very ▁specific ▁circumst ant ial ▁ab normal ities . ▁" Pro