What Does Kidney Functions Going Up To 49 Percent Indicate?

Question: I'm 67 years old tho have had both kidney stones bilateraly, as well as a couple of kidney infections, these were 20 years or so ago. I have been about 30-40 one overweight for the last 15 years and was diagnosed w/type 2 diabetes 2 years ago. It is barely in the realm of diabetes rather than pre diabetes and my blood sugar is almost always under 100. I also have had high blood pressure the last 10-15 years and high cholesterol the last 10 years. I've never smoked and have been tested thoroughly for cardiovascular disease with no evidence shown. I have had extensive digestive issues which is presumed to be e been IBS-d and more recently IBS-c. I've also developed both osteoporosis and chronic anemia which I am being treated for. I had taken p.o. Meds for both conditions for years with no results. I'm taking Prolia injections and iv iron infusions approximately every 3-4 months. Last month during routine testing prior to shoulder surgery for rotator cuff, my PCP, an internist discovered my creatinine level had jumped to 5.0. He called me immediately and ordered an ultrasound. I noticed on his orders he put acute renal failure under the dx. He had me discontinue a few of my meds and sent me to a nephrologist. Tho both Drs talked of admitting me my subsequent labs were lower 1.5 then even lower. He had started me on abx. I did a 24 hour blood and urine tests for nephrologist. After results I was told my kidney function was up to 49% from 44%. She explained the condition was likely many years in the making instead of an acute episode. My query is why would this just now show up in my labs. I have lab work pretty routinely bc of my anemia, osteoporosis, etc. I just add that the ortho surgeon had ordered a shoulder c.f. W/contrast just a few weeks ago. I'm concerned. Ty.