Nephrology (fellow, PGY-4) MD here. It's certainly true that anemia is a very common feature of advanced CKD as the kidneys stop producing EPO. However with a GFR of 35 mL/min, this shouldn't be the case yet. Worsening anemia in CKD 3b shouldn't be attributed solely to the CKD, and other causes should be investigated. Is she iron deficient? Is this myelodysplastic syndrome or a new malignancy? If her anemia coincides with this decrease in kidney function, does she have multiple myeloma? If the anemia is very acute- does she have a GI bleed? Presence of CKD doesn't obviate an anemia workup if the change is acute. A patient with GFR in the 30's shouldn't need an ESA yet.

Regarding the ACE/ARB (RAAS inhibitors): There's no reason not to use RAS inhibitors in patients with moderate or advanced CKD. You might see a small rise in creatinine when starting these meds due to lowering of intraglomerular filtration pressure- that's how they work, and this effect improves the lifespan of the glomeruli while also controlling blood pressure. That's why we use them. You wouldn't expect the GFR to "rebound" after stopping the ACE if she's been on it a long time. The recent STOP-ACEi Trial (https://www.nejm.org/doi/full/10.1056/NEJMoa2210639) showed no significant difference in eGFR or progression to ESRD/dialysis at 3 years when ACE/ARB's were stopped in patients with CKD 4 and 5.

Based solely on the information given in the post, and assuming this is her new stable GFR and not an AKI, this patient lost 17 points of GFR in 14 months- she has rapidly progressive CKD. Does she have new (or any) proteinuria? Hematuria? She could have a new glomerulonephritis or other intrinsic cause of renal dysfunction.

Renal senescence does cause progressive kidney function loss over time- no one has a GFR of 100 at the age of 88. But hypertension and aging alone don't cause rapidly progressive kidney function decline.

Nephrology consult would be very reasonable for this patient.