Urine Specific Gravity in Dogs: Normal Range & What Low USG Means

Urine specific gravity (USG) is one of the most informative values on a urinalysis — and one of the most commonly misunderstood. A single number tells your vet whether the kidneys are concentrating urine properly, and it can detect kidney disease before BUN and creatinine even budge.

What Is Urine Specific Gravity?

USG measures the density of urine relative to pure water (1.000). The kidneys add waste products, electrolytes, and other solutes to urine as they filter the blood — the more they concentrate, the higher the USG. A well-functioning kidney can produce urine as concentrated as 1.065 or more.

USG is measured with a refractometer, a handheld optical device that bends light through the sample. The dipstick pad for specific gravity on a urine reagent strip is unreliable in dogs and should never be used for clinical decisions — only refractometer readings count.

USG is always part of a complete urinalysis, which also includes protein, glucose, blood, pH, sediment exam, and other values. A USG result in isolation tells a partial story; your vet reads it alongside BUN, creatinine, and SDMA from the blood panel.

USG Interpretation Chart

The Most Important Distinction: Pre-Renal vs Renal

The single most valuable use of USG is distinguishing whether elevated BUN and creatinine are coming from the kidneys or from something else. This distinction changes treatment completely.

At least 66–75% of kidney nephrons must be lost before BUN and creatinine rise above normal — but loss of concentrating ability begins much earlier. A dog whose USG drops from 1.040 to 1.022 over 12 months may have perfectly normal bloodwork yet be losing significant kidney function. This is why annual urinalysis matters in senior dogs even when the blood panel looks clean.

Causes of Low or Dilute USG in Dogs

When USG is persistently below 1.030, the differential includes:

• • Cushing's disease — the most common hormonal cause. Excess cortisol blocks ADH, preventing water reabsorption. Typical USG 1.008–1.020 alongside PU/PD, pot-belly, and hair loss.
• • Chronic kidney disease (CKD) — as nephrons are lost the kidney can no longer create a concentration gradient. Isosthenuria (1.007–1.013) is the classic hallmark.
• • Diabetes insipidus — central DI (brain doesn't produce ADH) or nephrogenic DI (kidneys don't respond) both cause extreme hyposthenuria, often below 1.007, with enormous urine volumes.
• • Pyometra (intact females) — bacterial toxins block tubular ADH response, often the first detectable lab abnormality. Always rule out in an intact female with unexplained dilute urine.
• • Diabetes mellitus — glucosuria acts as an osmotic diuretic, drawing water into the tubules. USG is typically 1.015–1.030 with glucose visible on the dipstick.
• • Psychogenic polydipsia — compulsive water drinking (common in working breeds) dilutes urine by sheer volume. Chronic overconsumption causes medullary washout. A water deprivation test distinguishes it from true DI.
• • Hypercalcemia — high calcium directly interferes with tubular ADH response. Causes include lymphoma, hyperparathyroidism, and Addison's disease.
• • Liver disease — severe hepatic insufficiency reduces urea production, impairing the kidney's concentration gradient. Portosystemic shunt dogs frequently have dilute urine.

What Your Vet Will Do Next

Symptoms That May Accompany Low USG

Dogs with persistently dilute urine often show:

• • Excessive drinking (polydipsia) and frequent urination (polyuria)
• • Accidents in the house despite being house-trained
• • Pale, nearly colorless urine
• • Weight loss, decreased appetite (if CKD advancing)
• • Pot-belly, hair thinning (if Cushing's)
• • Lethargy and muscle wasting in later stages

Frequently Asked Questions