Echoing everyone else thoughts....I'm really sorry you're having to deal with this
As Murrydobe said, it's now all about support and quality of life.
The measurement you've given for billirubin is different to the way ours is measured....ie: Zil's was 16 when it should have been 4. That can be brought back down using Ursodiol (bile salts) which although expensive, seem to work pretty quickly. Also by starting a liver support diet, and prednisone/prednisolone. I only used the ursodiol when Zil's billirubin count was up (and dropped it from the regime when the count was in normal range)...he managed about 11 months from diagnosis....but it was a rollercoaster of an epic battle when he was in the acute stages and the progression of this disease seems to be quite an individual thing...although long term prognosis isn't good.
The exception seems to be if it's caught and controlled early...
If your dog is up to, it a biopsy really is the only way to conclusively know what's going on...but as Murraydobe said...it's a very high risk procedure, complicated by clotting and healing issues due to the compromised liver function. Be guided by the specialist's recommendation but make sure they advise you of the risks and a carefully considered opinion as to whether it is appropriate for your dog's individual case.
Regular blood tests are going to be a way of life for some time until you see a stabilised pattern. Also request fasting bile acid and protein screens to the full blood analysis ...it will give you some valuable fine tuning information.
In addition to the denmarin, Ursodiol and prednisolone, ranitidine (to prevent ulcers forming) and in later stages spironolactone if ascites forms, a liver support diet is going to be your main form of 'control'.
This involves switching to forms of protein that are easily digested and produce less ammonia as a byproduct of digestion. ie: no red meats. small amounts of chicken, turkey, and fish become the major sources of protein, in addition to cottage cheese and tofu. (I also tried amaranth with Zil, but he didn't appear to want to eat it). The inclusion of oatmeal is also extremely helpful as it absorbs excess ammonia and regulates motility/absorbtion rates through the intestine (which is also critical for avoiding excess ammonia). High ammonia levels can lead to HE (Hepatic encephalopaty....head tremors) and neurological complications.
The goal through medication and diet, is to simulate the function of the liver as a balancing/regulating organ. It's not easy to do and takes some time to find the right balance for each individual...which can also change on a daily basis initially...but hang in there and keep working on it, as it can be achieved to a certain extent.
As Chevy is already over 8 years old, this might not be the typical genetic form of CAH...or it might be a copper storage form...so the benefits of a biopsy could outweigh the risks...as you might have a chance of beating the odds. However I'm not a vet...so the specialist is really the only one who can advise you on this. Hopefully they will do x-rays and ultrasounds first to check for tumours, shunts and surface scarring of the liver.
I wouldn't wait until the specialist appointment to begin the ursodiol, prednisolone and denmarin...or the change in diet either. Get started on them straight away...especially the ursodiol.
Good luck, and we're all here as a moral support team. unfortunately this is an emotional rollercoaster of a condition and there's no easy or simple ways through it.
There are other little tweeks (herbal and diet) that can be tried as specific issues crop up and once you have a better picture of what the situation is from the specialist.
please keep us informed how chevy's going as we'll be praying for her.
