There is really no traditional "reference range" for specific gravity in
ferrets.  The specific gravity is a measur of the concentration of the
solids in urine, and can fluctuate widely based on the hydration status
of the animal at the time that the urine is obtained, as well as other
factors, such as the presence or absence of diabetes, functional state
of the kidney, etc.
 
The way we look at specific gravity is to see if the animal is able to
exceed a level of 1.030-1.035 - if this is not seen on a routine catch,
then we will take it again, and may even run a limited water deprivation
test to see if we can make it go up over this level.  If it does at any
time, for any reason, then you can safely assume that the kidney can
concentrate urine effectively.
 
Older kidneys, may be able to concentrate to 1.020 or so with out signs
of disease.  The problem occurs when the level constantly is at the
1.008-1.012 range.  This is the concentration of the blood that passes
through the kidney, and signifies that the kidney is not able to
concentrate the urine at all.  This finding, coupled with evidence of an
elevated BUN, creatine, and or phosphorus, indicate the presence of renal
failure.
 
A diagnosis of renal failure should always be based on all findings
evaluated in concert - the specific gravity of the urine, the urinalysis,
and the so-call renal enzymes in the blood (actually not enzymes, but
normal substances excreted by the kidney, such as BUN, creatinine, etc.
 
With kindest regards,
Bruce H. Williams, DVM, DACVP
 
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[Posted in FML issue 3435]