Urine specific gravity in dogs, values and why there is no normal range

What urine specific gravity measures

Urine specific gravity compares the weight of urine with the weight of pure water: the more dissolved material the urine carries, salts, urea, sometimes glucose, the higher the figure climbs. It is written without units, as 1.0 followed by a few digits, and appears on reports as specific gravity, SG or USG. It does not describe a disease but the work of the kidney, which concentrates urine when the body is short of water and dilutes it when the animal has drunk a lot.

Why there is no normal range for urine specific gravity

IRIS, the international veterinary society of reference on kidney disease in dogs and cats, states that any urine specific gravity value can be normal, because everything depends on how well hydrated the animal was when the sample was collected. The physiological spread is enormous, from 1.001 to over 1.075 in dogs and over 1.085 in cats, and IRIS reports that some dogs vary two to threefold within two hours.

In a normally hydrated animal, values often sit around 1.015 to 1.045 in dogs and 1.035 to 1.060 in cats, according to IRIS and veterinary diagnostic laboratories. Those are indicative orders of magnitude rather than norms, and only the range printed on your own report lets a result be placed at all. Cats concentrate their urine considerably more than dogs: a reading that looks unremarkable in a dog would be low in a cat.

The timing of collection therefore changes everything. The first urine of the morning, after a night without drinking, is the most concentrated, and it is usually the sample the vet asks for. Several treatments also dilute urine by design: intravenous fluids supply water in excess, a diuretic forces the kidney to get rid of it, and steroids increase both thirst and urine volume. In an animal on fluids or on those drugs, a low specific gravity says almost nothing about kidney function.

What vets explore when the urine is poorly concentrated

It is not the value on its own that raises a question, it is a combination. A working kidney has to concentrate urine when the body is short of water: if the animal is dehydrated, or if its blood urea and creatinine are raised, and the urine nevertheless stays poorly concentrated, that contradiction is the real piece of information, and it is there that the vet carries on. The middle zone, where urine is neither concentrated nor frankly dilute, around 1.008 to 1.012, is called isosthenuria and draws particular attention.

The commonest reason for running this test is the animal that drinks a lot and passes a lot of urine. The possible causes do not involve the kidney alone: blood sugar, hormones, the uterus in an unspayed female, calcium, the liver. Specific gravity then helps decide which direction to search in rather than settling anything, and it is read alongside the urine sediment, urea, creatinine and SDMA.

The urine protein to creatinine ratio, the other figure on the report

The urine protein to creatinine ratio, shortened to UPC, relates the protein leaking into the urine to urinary creatinine, which cancels out the effect of dilution. Unlike specific gravity, it does have thresholds. Below 0.2 an animal is considered non-proteinuric in both species. Above that, the IRIS scheme separates a borderline zone from frank proteinuria, and the threshold differs by species: in dogs the borderline zone runs from 0.2 to 0.5 and proteinuria begins above 0.5, while in cats it runs from 0.2 to 0.4 and proteinuria begins above 0.4. A ratio of 0.45 therefore reads differently in the two species. The figure is only interpretable if the urine sediment is quiet, with no infection, blood or inflammation, and it is confirmed on two to three samples about two weeks apart.

What this figure does not tell you on its own

A single specific gravity reading supports no conclusion, reassuring or worrying: concentrated urine does not rule out kidney disease, and dilute urine in an animal that has drunk a lot proves nothing at all. Urine dipsticks often carry a specific gravity pad, but that pad is not reliable in dogs and cats because it was developed for human urine. The right instrument is the veterinary refractometer, which has separate scales for dogs and for cats: the same sample read on the wrong scale gives a false figure. Only the vet examining your animal can connect this figure to what they find.

Questions to ask your vet

1. Was my animal properly hydrated when the sample was taken?
2. Was the urine a morning sample, and how was it collected?
3. Was the specific gravity measured on a refractometer, on the scale for its species?
4. How does this figure fit with my animal's urea, creatinine and SDMA?
5. Could a current treatment, intravenous fluids, a diuretic or steroids, explain this result?

What is a normal urine specific gravity in dogs?

There is no norm in the usual sense. IRIS, the international veterinary society of reference on kidney disease in dogs and cats, states that any value can be normal depending on how well hydrated the animal was when the sample was collected. In a normally hydrated dog, values often sit around 1.015 to 1.045, and in a cat around 1.035 to 1.060, but those are indicative orders of magnitude rather than limits to be met. Only the range printed on your own report, which reflects the laboratory's method, can place a result, and even that is not enough to judge it.

What does low urine specific gravity mean in a dog?

On its own it means nothing. A dog that drinks a lot, eats wet food, or is receiving intravenous fluids, a diuretic or steroids normally produces dilute urine, and its kidney is not at fault. What draws a vet's attention is poorly concentrated urine in an animal that is dehydrated, or alongside raised blood urea and creatinine, because a working kidney has to concentrate urine when the body is short of water. That contradiction leads to further investigation, never to a conclusion based on the specific gravity alone.

How does urine specific gravity differ between dogs and cats?

Cats concentrate their urine considerably more than dogs, and that species difference changes how a result reads. In normally hydrated animals the indicative order of magnitude is roughly 1.015 to 1.045 in dogs against 1.035 to 1.060 in cats, and the physiological spread goes beyond 1.075 in dogs and 1.085 in cats. A value that would pass unnoticed in a dog can be low in a cat. This is why veterinary refractometers carry two separate scales, one for each species.

Can a urine dipstick measure specific gravity reliably?

No. The specific gravity pad on urine dipsticks was developed for human urine and is not reliable in dogs and cats. The right instrument is the veterinary refractometer, with separate scales for the two species, and it is what produces the figure quoted on a properly done report. The dipstick remains useful for other parameters, protein, blood, glucose and pH, but specific gravity is measured differently, and a dipstick result should not be compared with a refractometer result.