If and when he goes to MEPS, he will be evaluated and they will let him know. I believe that as long as your friend hasn't had any kidney stones for atleast a year prior to being commissioned, then he's fine. From personal experience, I've had a kidney stone back in 99. They're painful and take a while to pass. I was a MEPS last month and I was told that I was medically cleared. Tell your friend to start filtering his water, or just drink bottled water to prevent future stones. Also, he should strain his urine to see if he has passed the stone or if there are signs of blood. If he sees little blood clots, then it's very possible that he will get an infection. He needs to monitor it closely.