Donovan McNabb's DUI arrest just got extreme -- because cops say his blood alcohol level was more than TWICE the legal limit when he was arrested ... TMZ Sports has learned.
As we previously reported, the former NFL superstar was popped in Arizona on June 28 after crashing into another car on the way home from a sports bar.
McNabb INSISTED he had nothing to drink that night -- claiming he had just had some cough medicine to fight a cold.
But the officials tell TMZ Sports .... the results from McNabb's blood test are in -- and he registered a .17 ... more than DOUBLE the legal limit, .08.
In fact, anything higher than a .15 in Arizona constitutes an "extreme DUI" -- which brings stiffer penalties if convicted ... especially since it's McNabb's 2nd DUI in Arizona in less than 2 years.