"Adequate" Urine Concentration USG in Azotemia USG Species Pre-renal Renal Canine >1.030 <1.030 Feline >1.035 <1.035 Equine/Bovine >1.025 <1.025 In this context, an "adequate" USG indicates the existence of sufficient functional nephrons to adequately concentrate the urine and to prevent development of azotemia, provided that renal blood flow is sufficient and that the ability of those nephrons to concentrate urine is not impaired by other factors. In nephropathies characterized by progressive loss of of functional nephrons, the ability to concentrate urine is compromised when about 2/3 of the nephron mass is lost. Clearance of nitrogenous waste products sufficient to prevent azotemia, however, persists until roughly 3/4 of functional nephrons are lost. Therefore, if azotemia is due to loss of nephron mass (>3/4 loss, i.e., renal failure), ability to concentrate urine will have already been lost (USG <"adequate" for species). An exeption to this occurs in cats, in which glomerular disease (and azotemia) can precede loss of concentrating ability. In a primary renal azotemia, the kidney cannot concentrate or dilute urine, so there is often a fixed (constant) isosthenuric USG, i.e. USG of 1.008-1.012. However, in renal disease, the total loss of renal tubule function occurs gradually, therefore USGs between isosthenuric and "adequate" ranges in animals, with dehydration and/or azotemia, are highly suggestive of primary renal failure. Last Updated: January 15th, 1999