Wanted to put my 2 cents since I have some experience in this area. I’m 10 yrs. post kidney transplant and over the years have gone through all types of tests.
So here’s my take. Get the results. The ‘75% function’ your doc is talking about is likely the eGFR which is a calculated value of how well you kidney is filtering waste. This value is obtained from a formula using your serum creatinine, age, sex and race. To be honest this value is, to a certain degree ‘useless’. I’ve seen a person with normal creatinine level (so a good eGFR) have a bad actual GFR, and a person with a less than desirable creatinine & eGFR with a good actual GFR.
Getting the actual hard copy results of your labs and looking at the creatinine will give you an good idea of what is happening. If it is within the normal range, that’s a good start. You can get ready to start arguing with your doc. If it isn’t you may or may not have issues with your kidney. So you may want to at least give her a listen.
If your creatinine isn’t in the normal range you will probably want to check to verify if something is really happening. This can be done by getting a 24 hr creatinine clearance where you pee and collect urine for 24 hours, or via nuclear GFR which gets your actual GFR and is not a calculated value. The first is cheaper but really a pain in the ass. The second takes about 5 minutes but is considerably more expensive. You may also want to see your urinalysis if there is protein in your urine. Protein in urine may be a sign your kidney isn’t functioning as well as you’d want, because it has ‘holes’ that is allowing protein to spill out of it and into your urine.
As I said a bit back, your kidneys may be ok even if creatinine is above normal. The reason? Being heavier you have more muscle mass, which does make creatinine for some people go above the normal range, thus look abnormal (so less than desirable kidney %). Many big bodybuilders experience this, but have normal kidney health. Problem is unless you further check you can’t be sure. Also eating tons of protein, or taking creatine or drugs like certain pain killers can increase the level. This is why your doc wants you to cut back.
You may want to be careful on taking in excessive protein, and creatinine until you get to the bottom of things (this may be a false alarm or it may be an early warning). If one’s kidneys are healthy, no problem, they can adjust and take a high protein diet. But if they happen to be weaker or predisposed genetically, the high protein and creatine intake can destroy the kidneys. Problem is, one can never know if they born with weaker than normal kidneys, unless they do regular tests because the way it behaves is it starts out at an ok level, and slowly deteriorated over time . The weird thing about kidneys are, if they are healthy, high protein diet is ok and doesn’t hurt them, but if the kidneys have even slight issues, the high protein diet will slowly cause the kidneys to deteriorate.
Think of your kidneys as big fishing nets, and all protein and other stuff you ingest go in. If the kidneys are healthy, the fish net has no holes, so even a big inflow of protein from a high protein diet, the kidney is strong enough to handle (but to also only to a certain degree before it starts to get overburdened). But if your kidneys aren’t totally healthy, be it from birth, or from trauma (being hit hard) or anything else. It is like a fishing net with a hole. The hole will be very small at the start, but like a net where you keep pushing a lot of protein in it will slowly keep tearing at the hole and you will see the kidney function slowly come down year by year as the ‘hole’ increases.
The only way to know if you have weak kidneys is to do the labs. Because kidney trouble is silent, like high blood pressure. Unless you get checked by the time you feel the effects it’s already quite bad.
Getting the results will tell you what your next move is. As for your weight, it will only come to play if your kidneys aren’t ok.
Hope this helps.