Dear Deanna:
 
>I need some information about kidney failure and I haven't been able to
>find much on the internet.  Please help me to understand this so that I
>may help my baby.  What is it exactly?  Is there a cure?  Is it painful?
>What is the life expectancy once diagnosed?  Is she going to die?
 
Renal failure is a common finding in older ferrets due to the kidneys
lack of significant regenerative capacity.  As all animals age, including
humans, as kidney tissue wears out, it is not replaced by more kidney
tissue, but by fibrous connective tissue, which doesn't do anything (just
takes up space, like a scar.) Over a lifetime, we continually lose renal
tissue, and our kidneys lose ability to perform necessary tasks, such as
to filter waste into the urine, and reclaim water as necessary to maintain
proper hydration.  As we get older, this is manifested by having to urinate
more frequently, etc.  This is normal.
 
Chronic renal failure occurs when the process progresses to the point where
there is so little functioning renal tissue that the substances which
normally are excreted by the kidney, are no longer excreted, and build up
into the blood.  Because renal tissue is replaced by scar tissue, there is
no hope of recovery.  Early in the process, remaining kidney tissue is able
to undergo hypertrophy and function at a more higher level, but eventually,
even this hyperfunctional tissue is lost.  When 90% of renal tissue is
lost, fatal chronic renal failure occurs.  (For those of you who remember
this particular subject discussed in October, you may notice that the
amount of tissue that can be lost has risen from 75% to 90%.  This change
is the result of an excellent lecture I recently attended at the Veterinary
Pathologist's conference earlier this month, which actually now factors in
the effect of nephron hypertrophy in chronic renal failure.)
 
How do you measure renal failure?  In general, by measuring certain blood
and urine parameters which only go awry once critical renal mass is lost.
After around 66% of the kidneys are lost, you lose the ability to
concentrate urine.  Measurements of the specific gravity of the kidneys
will be low and the animal's frequency of urination will increase.
However, very few of us watch closely enough to pick up the early signs.
After 90% of the kidney is lost, certain substances which are normally
excreted by functional kidneys tend to back up and are present in increased
levels in the blood - urea, creatinine, and phosphorus - which can be
picked up by routine blood tests.  As the level of blood urea nitrogen
(BUN) increases, the animal will start to feel ill and may go off food.
Intractable pain has not been described by human patients in renal failure,
but some non-specific aches (like we get with the flu) may occur.  This is
probably the first obvious sign of renal failure that is seen by owners.
Severely increased BUN may result in an ammonia smell to the breath and
the presence of mouth ulcers (which are far more rare in ferrets than in
dogs or cats with renal failure.)
 
There really is no cure for chronic renal failure, as that tissue will
never be replaced, only palliative treatment designed to decrease levels
of toxic substances in the blood and thus clinical signs.  When the levels
are high, large amounts of intravenous or subcutaneous fluids will help to
flush out some of these substances and decrease the levels.  They will of
course, build up again over time, with animals with less functional renal
tissue having faster increases.
 
Common wisdom in veterinary medicine suggests that lower protein diets are
renal-sparing, and we generally reduce protein content markedly in the
diets of animals with renal failure.  As a precaution in cats and ferrets,
two species who suffer inordinately high rates of renal failure as a
species, it is probably a good idea to decrease feed protein at the times
when renal changes are first seen microscopically - about 3.5 years in
ferrets.  At or arond that age, I personally change my ferrets over to
adult cat maintenance feeds and Totally Ferret geriatric food.
 
With kindest regards,
Bruce Williams, dVM
[Posted in FML issue 3267]