Hello,
It appears you have started thorough work-up.
Has the stool been tested for parsites and /or fatty content?
Was a thyroid test done?
stool not tested, a recent observation
I don't think thyroid evaluated
Is your dog intact or neutered?
Did they send the urine out to be cultured?
neutered (retired racedog)
I believe culture was an appropriate low colony count
If this is an acute onset even with the US changes to the kidneys I would consider a toxin possibility. I would recommend placing the pet on IV fluids and re-evaluating the blood work and image of the kidneys in 24hrs. If there are no improvements consider a kidney biopsy after checking the clotting profile.
not acute onset, approx 4 months of drinking and increased urination. initally atributed to heat, but obviously not the case.
is there a diferential diagnosis?
cancer?
immune mediated process? Inflammatory markers in liver and kidneys (lab and echo findings)
hematologic condition? (positive coombs)
GI souces?
psychogenic??
there definitely has been some weight loss though appears to eat normally
The "positive" coombs may be false or immune response because there is no anemia. A positive can simply mean that there is a immune reaction to the red blood cells so I am less concerned with any hematologic condition.
As also with psychogenic because of the weight loss which is not usually seen with that disorder.
As to GI sources, you stated that the appetite has remained normal and the diarrhea is a recent occurrence suggesting that this may be a secondary response and possibly not the primary cause.
An immune mediated, viral or cancerous cause are all very reasonable and still believe that your final diagnosis lays with obtaining a tissue sample.
You also mentioned that an ACTH stim test was normal, how long ago was that done and have you considered repeating it as this presentation could be atypical Cushing's.
I hope this has been helpful for you.
Emergency Clinician
15+years vet care: Emergency/Critical Care small animals