Drop in eGFR? Should we be worried?

[Zessira]

My husband is 33 and Caucasian. He had a kidney stone in October 2018, and subsequently diagnosed with a uretal stricture on his left side. He had a stent placed for a week or two. Severe pain with that, urologist said it was ureteric colic. Stent removed, and he seemed fine. His eGFR was 92 in May 2018. It was 113 in December of 2018, and now in May 2019, it's 89. That's quite a drop from December to now. He had a tooth infection recently and took a lot of Ibuprofen for this, which might be the cause, but I'm also worried that maybe the cause could be hydronephrosis and the stent didn't work? Our appointment with the urologist is still a few weeks out. Bun/creatinine ratio 11, creatinine 1.09, BUN 12. Oh, and he also has benign prostatic hyperplasia, and isn't diabetic. Thank you.