Hello,
I would generally allow patients taking ACEi or ARBs to stay on these medications if, while one them, the potassium remains below 6. I would not start them or increase their dose if they already have potassium levels in the 5-6 mmol/L range. I would also ensure that the patients continue to follow a potassium restricted diet, linked below.
As for further investigations of the proteinuria, it seems that 22 years of diabetes could account for it, particularly if glycemic control has not been adequate over the years. But if there was extreme proteinuria (> 5 grams/day), if significant hematuria or an active urine was present, or signs of systemic disease, then perhaps further investigation would be warranted.
Dr. Jordan Weinstein