Is a gfr level of 89 ml/min/1.73m2 a concern?

Depends: At age 23, your GFR should be 120 ml/ min, however, many factors make a difference. For instance, your GFR equation may underestimate you actual function if you are of a muscular built and may overestimate if your lean body mass is small but weight is high d/t hi fat content. You need a 24 hour urine collection to be done for creat clearance (gfr check).Make sure urine's negative blood & protein.