Urine specific gravity (USG)
Urine ·Also called: USG, specific gravity, SG, urine concentration, isosthenuria
What it is
Specific gravity compares urine with pure water. Water is 1.000; the more dissolved waste the kidneys have packed into a given volume, the higher the number. It is measured with a refractometer on a drop of urine.
Why your vet measures it
Concentrating urine is one of the first abilities kidneys lose. A dog or cat producing urine stuck around 1.008 to 1.012 — the same concentration as blood plasma, called isosthenuria — has kidneys that are no longer concentrating, and that finding alongside a raised creatinine is what distinguishes kidney disease from simple dehydration.
What a high result can mean
- Dehydration, where healthy kidneys are correctly conserving water
- Reduced fluid intake, or fluid loss through vomiting and diarrhoea
- A normal, healthy finding in a well-hydrated cat — cats concentrate urine very effectively
What a low result can mean
- Chronic kidney disease, where the concentrating ability is lost
- Excess drinking from diabetes, Cushing's disease, or hyperthyroidism
- A womb infection (pyometra) in an unspayed female
- Diuretic or steroid treatment
- Recent intravenous fluids, or simply a large drink beforehand
Dogs and cats differ
Cats evolved as desert animals and concentrate urine far more strongly than dogs — a healthy cat often exceeds 1.040. A cat producing consistently dilute urine is therefore a more pointed finding than the same value in a dog, where 1.025 can be perfectly normal in a well-hydrated animal that has just had a big drink.
Questions worth asking your vet
- Was this urine sample collected before or after fluids were given?
- Do the blood kidney values and this urine concentration agree?
- Is my pet drinking noticeably more than usual at home?
Related terms
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